Merge from Chromium at DEPS revision r213057

This commit was generated by merge_to_master.py.

Change-Id: I3e2e2506eb9b0080157e9c5f133559df3e600388

34 files changed, 338 insertions, 34 deletions

diff --git a/sync/engine/sync_scheduler_impl.cc b/sync/engine/sync_scheduler_impl.cc
index fe377d4019..3a904d1dc5 100644
--- a/sync/engine/sync_scheduler_impl.cc
+++ b/sync/engine/sync_scheduler_impl.cc
@@ -616,7 +616,8 @@ void SyncSchedulerImpl::UpdateNudgeTimeRecords(ModelTypeSet types) {
 void SyncSchedulerImpl::AdjustPolling(PollAdjustType type) {
   DCHECK(CalledOnValidThread());
 
-  TimeDelta poll  = (!session_context_->notifications_enabled()) ?
+  TimeDelta poll  = (!session_context_->notifications_enabled() ||
+                     !session_context_->ShouldFetchUpdatesBeforeCommit()) ?
       syncer_short_poll_interval_seconds_ :
       syncer_long_poll_interval_seconds_;
   bool rate_changed = !poll_timer_.IsRunning() ||
diff --git a/sync/engine/sync_scheduler_unittest.cc b/sync/engine/sync_scheduler_unittest.cc
index a55eb7f1bb..3fb2042fe0 100644
--- a/sync/engine/sync_scheduler_unittest.cc
+++ b/sync/engine/sync_scheduler_unittest.cc
@@ -150,6 +150,7 @@ class SyncSchedulerTest : public testing::Test {
             &extensions_activity_monitor_,
             std::vector<SyncEngineEventListener*>(), NULL, NULL,
             true,  // enable keystore encryption
+            false,  // force enable pre-commit GU avoidance
             "fake_invalidator_client_id"));
     context_->set_routing_info(routing_info_);
     context_->set_notifications_enabled(true);
diff --git a/sync/engine/syncer.cc b/sync/engine/syncer.cc
index 8ebbff1170..8005459fb8 100644
--- a/sync/engine/syncer.cc
+++ b/sync/engine/syncer.cc
@@ -64,14 +64,17 @@ bool Syncer::NormalSyncShare(ModelTypeSet request_types,
                              SyncSession* session) {
   HandleCycleBegin(session);
   VLOG(1) << "Downloading types " << ModelTypeSetToString(request_types);
-  if (!DownloadAndApplyUpdates(
-          session,
-          base::Bind(&NormalDownloadUpdates,
-                     session,
-                     kCreateMobileBookmarksFolder,
-                     request_types,
-                     base::ConstRef(nudge_tracker)))) {
-    return HandleCycleEnd(session);
+  if (nudge_tracker.IsGetUpdatesRequired() ||
+      session->context()->ShouldFetchUpdatesBeforeCommit()) {
+    if (!DownloadAndApplyUpdates(
+            session,
+            base::Bind(&NormalDownloadUpdates,
+                       session,
+                       kCreateMobileBookmarksFolder,
+                       request_types,
+                       base::ConstRef(nudge_tracker)))) {
+      return HandleCycleEnd(session);
+    }
   }
 
   VLOG(1) << "Committing from types " << ModelTypeSetToString(request_types);
diff --git a/sync/engine/syncer_unittest.cc b/sync/engine/syncer_unittest.cc
index 61f7f9b838..a2ccccfb23 100644
--- a/sync/engine/syncer_unittest.cc
+++ b/sync/engine/syncer_unittest.cc
@@ -239,6 +239,7 @@ class SyncerTest : public testing::Test,
             &extensions_activity_monitor_,
             listeners, NULL, &traffic_recorder_,
             true,  // enable keystore encryption
+            false,  // force enable pre-commit GU avoidance experiment
             "fake_invalidator_client_id"));
     context_->set_routing_info(routing_info);
     syncer_ = new Syncer();
diff --git a/sync/internal_api/internal_components_factory_impl.cc b/sync/internal_api/internal_components_factory_impl.cc
index f4fd94232e..1cc3b112c6 100644
--- a/sync/internal_api/internal_components_factory_impl.cc
+++ b/sync/internal_api/internal_components_factory_impl.cc
@@ -48,6 +48,8 @@ InternalComponentsFactoryImpl::BuildContext(
           listeners, debug_info_getter,
           traffic_recorder,
           switches_.encryption_method == ENCRYPTION_KEYSTORE,
+          switches_.pre_commit_updates_policy ==
+              FORCE_ENABLE_PRE_COMMIT_UPDATE_AVOIDANCE,
           invalidation_client_id));
 }
 
diff --git a/sync/internal_api/public/base/invalidation.cc b/sync/internal_api/public/base/invalidation.cc
index 472fad2c3c..b503d07c4a 100644
--- a/sync/internal_api/public/base/invalidation.cc
+++ b/sync/internal_api/public/base/invalidation.cc
@@ -64,19 +64,23 @@ AckHandle::AckHandle(const std::string& state, base::Time timestamp)
 AckHandle::~AckHandle() {
 }
 
+const int64 Invalidation::kUnknownVersion = -1;
+
 Invalidation::Invalidation()
-    : ack_handle(AckHandle::InvalidAckHandle()) {
+    : version(kUnknownVersion), ack_handle(AckHandle::InvalidAckHandle()) {
 }
 
 Invalidation::~Invalidation() {
 }
 
 bool Invalidation::Equals(const Invalidation& other) const {
-  return (payload == other.payload) && ack_handle.Equals(other.ack_handle);
+  return (version == other.version) && (payload == other.payload) &&
+      ack_handle.Equals(other.ack_handle);
 }
 
 scoped_ptr<base::DictionaryValue> Invalidation::ToValue() const {
   scoped_ptr<base::DictionaryValue> value(new base::DictionaryValue());
+  value->SetString("version", base::Int64ToString(version));
   value->SetString("payload", payload);
   value->Set("ackHandle", ack_handle.ToValue().release());
   return value.Pass();
@@ -84,6 +88,13 @@ scoped_ptr<base::DictionaryValue> Invalidation::ToValue() const {
 
 bool Invalidation::ResetFromValue(const base::DictionaryValue& value) {
   const base::DictionaryValue* ack_handle_value = NULL;
+  std::string version_as_string;
+  if (value.GetString("version", &version_as_string)) {
+    if (!base::StringToInt64(version_as_string, &version))
+      return false;
+  } else {
+    version = kUnknownVersion;
+  }
   return
       value.GetString("payload", &payload) &&
       value.GetDictionary("ackHandle", &ack_handle_value) &&
diff --git a/sync/internal_api/public/base/invalidation.h b/sync/internal_api/public/base/invalidation.h
index e1e274ed13..851dbed747 100644
--- a/sync/internal_api/public/base/invalidation.h
+++ b/sync/internal_api/public/base/invalidation.h
@@ -43,11 +43,14 @@ class SYNC_EXPORT AckHandle {
 };
 
 // Represents a local invalidation, and is roughly analogous to
-// invalidation::Invalidation. It contains a payload (which may be empty) and an
+// invalidation::Invalidation. It contains a version (which may be
+// kUnknownVersion), a payload (which may be empty) and an
 // associated ack handle that an InvalidationHandler implementation can use to
 // acknowledge receipt of the invalidation. It does not embed the object ID,
 // since it is typically associated with it through ObjectIdInvalidationMap.
 struct SYNC_EXPORT Invalidation {
+  static const int64 kUnknownVersion;
+
   Invalidation();
   ~Invalidation();
 
@@ -56,6 +59,7 @@ struct SYNC_EXPORT Invalidation {
   scoped_ptr<base::DictionaryValue> ToValue() const;
   bool ResetFromValue(const base::DictionaryValue& value);
 
+  int64 version;
   std::string payload;
   AckHandle ack_handle;
 };
diff --git a/sync/internal_api/public/base/model_type.h b/sync/internal_api/public/base/model_type.h
index 59f970fd86..247d351375 100644
--- a/sync/internal_api/public/base/model_type.h
+++ b/sync/internal_api/public/base/model_type.h
@@ -207,6 +207,14 @@ SYNC_EXPORT ModelTypeSet ControlTypes();
 // See comment above for more information on what makes these types special.
 SYNC_EXPORT bool IsControlType(ModelType model_type);
 
+// Core types are those data types used by sync's core functionality (i.e. not
+// user data types). These types are always enabled, and include ControlTypes().
+//
+// The set of all core types.
+SYNC_EXPORT ModelTypeSet CoreTypes();
+// Those core types that have high priority (includes ControlTypes()).
+SYNC_EXPORT ModelTypeSet PriorityCoreTypes();
+
 // Determine a model type from the field number of its associated
 // EntitySpecifics field.  Returns UNSPECIFIED if the field number is
 // not recognized.
diff --git a/sync/internal_api/public/internal_components_factory.h b/sync/internal_api/public/internal_components_factory.h
index 6b79ddd2f9..96fd640737 100644
--- a/sync/internal_api/public/internal_components_factory.h
+++ b/sync/internal_api/public/internal_components_factory.h
@@ -50,6 +50,16 @@ class SYNC_EXPORT InternalComponentsFactory {
     BACKOFF_SHORT_INITIAL_RETRY_OVERRIDE
   };
 
+  enum PreCommitUpdatesPolicy {
+    // By default, the server will enable or disable this experiment through the
+    // sync protocol's experiments data type.
+    SERVER_CONTROLLED_PRE_COMMIT_UPDATE_AVOIANCE,
+
+    // This flag overrides the server's decision and enables the pre-commit
+    // update avoidance experiment.
+    FORCE_ENABLE_PRE_COMMIT_UPDATE_AVOIDANCE,
+  };
+
   // Configuration options for internal components. This struct is expected
   // to grow and shrink over time with transient features / experiments,
   // roughly following command line flags in chrome. Implementations of
@@ -58,6 +68,7 @@ class SYNC_EXPORT InternalComponentsFactory {
   struct Switches {
     EncryptionMethod encryption_method;
     BackoffOverride backoff_override;
+    PreCommitUpdatesPolicy pre_commit_updates_policy;
   };
 
   virtual ~InternalComponentsFactory() {}
diff --git a/sync/internal_api/public/util/experiments.h b/sync/internal_api/public/util/experiments.h
index 6c53e30120..144687d968 100644
--- a/sync/internal_api/public/util/experiments.h
+++ b/sync/internal_api/public/util/experiments.h
@@ -11,6 +11,7 @@ namespace syncer {
 
 const char kAutofillCullingTag[] = "autofill_culling";
 const char kFaviconSyncTag[] = "favicon_sync";
+const char kPreCommitUpdateAvoidanceTag[] = "pre_commit_update_avoidance";
 
 // A structure to hold the enable status of experimental sync features.
 struct Experiments {
diff --git a/sync/internal_api/sync_manager_impl.cc b/sync/internal_api/sync_manager_impl.cc
index e9eeea1832..3d6158d8a1 100644
--- a/sync/internal_api/sync_manager_impl.cc
+++ b/sync/internal_api/sync_manager_impl.cc
@@ -1295,6 +1295,17 @@ bool SyncManagerImpl::ReceivedExperiment(Experiments* experiments) {
     found_experiment = true;
   }
 
+  ReadNode pre_commit_update_avoidance_node(&trans);
+  if (pre_commit_update_avoidance_node.InitByClientTagLookup(
+          syncer::EXPERIMENTS,
+          syncer::kPreCommitUpdateAvoidanceTag) == BaseNode::INIT_OK) {
+    session_context_->set_server_enabled_pre_commit_update_avoidance(
+        pre_commit_update_avoidance_node.GetExperimentsSpecifics().
+            pre_commit_update_avoidance().enabled());
+    // We don't bother setting found_experiment.  The frontend doesn't need to
+    // know about this.
+  }
+
   return found_experiment;
 }
 
diff --git a/sync/internal_api/test/test_internal_components_factory.cc b/sync/internal_api/test/test_internal_components_factory.cc
index beb249e743..154c58cc99 100644
--- a/sync/internal_api/test/test_internal_components_factory.cc
+++ b/sync/internal_api/test/test_internal_components_factory.cc
@@ -45,6 +45,8 @@ TestInternalComponentsFactory::BuildContext(
           empty_listeners, debug_info_getter,
           traffic_recorder,
           switches_.encryption_method == ENCRYPTION_KEYSTORE,
+          switches_.pre_commit_updates_policy ==
+              FORCE_ENABLE_PRE_COMMIT_UPDATE_AVOIDANCE,
           invalidator_client_id));
 
 }
diff --git a/sync/notifier/object_id_invalidation_map.cc b/sync/notifier/object_id_invalidation_map.cc
index 47b08e684a..3dc7514b97 100644
--- a/sync/notifier/object_id_invalidation_map.cc
+++ b/sync/notifier/object_id_invalidation_map.cc
@@ -22,10 +22,11 @@ ObjectIdSet ObjectIdInvalidationMapToSet(
 }
 
 ObjectIdInvalidationMap ObjectIdSetToInvalidationMap(
-    const ObjectIdSet& ids, const std::string& payload) {
+    const ObjectIdSet& ids, int64 version, const std::string& payload) {
   ObjectIdInvalidationMap invalidation_map;
   for (ObjectIdSet::const_iterator it = ids.begin(); it != ids.end(); ++it) {
     // TODO(dcheng): Do we need to provide a way to set AckHandle?
+    invalidation_map[*it].version = version;
     invalidation_map[*it].payload = payload;
   }
   return invalidation_map;
diff --git a/sync/notifier/object_id_invalidation_map.h b/sync/notifier/object_id_invalidation_map.h
index 6560b3b51a..0a6a95ede4 100644
--- a/sync/notifier/object_id_invalidation_map.h
+++ b/sync/notifier/object_id_invalidation_map.h
@@ -8,6 +8,7 @@
 #include <map>
 #include <string>
 
+#include "base/basictypes.h"
 #include "base/memory/scoped_ptr.h"
 #include "google/cacheinvalidation/include/types.h"
 #include "sync/base/sync_export.h"
@@ -29,7 +30,7 @@ typedef std::map<invalidation::ObjectId,
 ObjectIdSet ObjectIdInvalidationMapToSet(
     const ObjectIdInvalidationMap& invalidation_map);
 SYNC_EXPORT ObjectIdInvalidationMap ObjectIdSetToInvalidationMap(
-    const ObjectIdSet& ids, const std::string& payload);
+    const ObjectIdSet& ids, int64 version, const std::string& payload);
 
 SYNC_EXPORT bool ObjectIdInvalidationMapEquals(
     const ObjectIdInvalidationMap& invalidation_map1,
@@ -51,4 +52,4 @@ SYNC_EXPORT ObjectIdInvalidationMap
 
 }  // namespace syncer
 
-#endif  // HOME_DCHENG_SRC_CHROMIUM_SRC_SYNC_NOTIFIER_OBJECT_ID_STATE_MAP_H_
+#endif  // SYNC_NOTIFIER_OBJECT_ID_INVALIDATION_MAP_H_
diff --git a/sync/notifier/p2p_invalidator.cc b/sync/notifier/p2p_invalidator.cc
index 8b54c0417e..05ec183537 100644
--- a/sync/notifier/p2p_invalidator.cc
+++ b/sync/notifier/p2p_invalidator.cc
@@ -173,7 +173,9 @@ void P2PInvalidator::UpdateRegisteredIds(InvalidationHandler* handler,
   const P2PNotificationData notification_data(
       invalidator_client_id_,
       NOTIFY_SELF,
-      ObjectIdSetToInvalidationMap(new_ids, std::string()));
+      ObjectIdSetToInvalidationMap(new_ids,
+                                   Invalidation::kUnknownVersion,
+                                   std::string()));
   SendNotificationData(notification_data);
 }
 
@@ -228,6 +230,7 @@ void P2PInvalidator::OnNotificationsEnabled() {
         invalidator_client_id_,
         NOTIFY_SELF,
         ObjectIdSetToInvalidationMap(registrar_.GetAllRegisteredIds(),
+                                     Invalidation::kUnknownVersion,
                                      std::string()));
     SendNotificationData(notification_data);
   }
@@ -263,6 +266,7 @@ void P2PInvalidator::OnIncomingNotification(
         invalidator_client_id_,
         NOTIFY_ALL,
         ObjectIdSetToInvalidationMap(registrar_.GetAllRegisteredIds(),
+                                     Invalidation::kUnknownVersion,
                                      std::string()));
   }
   if (!notification_data.IsTargeted(invalidator_client_id_)) {
diff --git a/sync/notifier/p2p_invalidator_unittest.cc b/sync/notifier/p2p_invalidator_unittest.cc
index 6acc3d1703..be9ee3f970 100644
--- a/sync/notifier/p2p_invalidator_unittest.cc
+++ b/sync/notifier/p2p_invalidator_unittest.cc
@@ -180,6 +180,7 @@ TEST_F(P2PInvalidatorTest, P2PNotificationDataNonDefault) {
   const ObjectIdInvalidationMap& invalidation_map =
       ObjectIdSetToInvalidationMap(
           ModelTypeSetToObjectIdSet(ModelTypeSet(BOOKMARKS, THEMES)),
+          Invalidation::kUnknownVersion,
           std::string());
   const P2PNotificationData notification_data(
       "sender", NOTIFY_ALL, invalidation_map);
@@ -193,10 +194,10 @@ TEST_F(P2PInvalidatorTest, P2PNotificationDataNonDefault) {
       "{\"idInvalidationMap\":["
       "{\"objectId\":{\"name\":\"BOOKMARK\",\"source\":1004},"
       "\"state\":{\"ackHandle\":{\"state\":\"\",\"timestamp\":\"0\"},"
-      "\"payload\":\"\"}},"
+      "\"payload\":\"\",\"version\":\"-1\"}},"
       "{\"objectId\":{\"name\":\"THEME\",\"source\":1004},"
       "\"state\":{\"ackHandle\":{\"state\":\"\",\"timestamp\":\"0\"},"
-      "\"payload\":\"\"}}"
+      "\"payload\":\"\",\"version\":\"-1\"}}"
       "],\"notificationType\":\"notifyAll\","
       "\"senderId\":\"sender\"}", notification_data_str);
 
@@ -249,6 +250,7 @@ TEST_F(P2PInvalidatorTest, NotificationsBasic) {
     const ObjectIdInvalidationMap& invalidation_map =
         ObjectIdSetToInvalidationMap(
             ModelTypeSetToObjectIdSet(ModelTypeSet(THEMES, APPS)),
+            Invalidation::kUnknownVersion,
             std::string());
     invalidator->SendInvalidation(invalidation_map);
   }
@@ -267,6 +269,7 @@ TEST_F(P2PInvalidatorTest, SendNotificationData) {
 
   const ObjectIdInvalidationMap& invalidation_map =
       ObjectIdSetToInvalidationMap(ModelTypeSetToObjectIdSet(changed_types),
+                                   Invalidation::kUnknownVersion,
                                    std::string());
 
   P2PInvalidator* const invalidator = delegate_.GetInvalidator();
diff --git a/sync/notifier/sync_invalidation_listener.cc b/sync/notifier/sync_invalidation_listener.cc
index ddb9e35184..ed07f2070b 100644
--- a/sync/notifier/sync_invalidation_listener.cc
+++ b/sync/notifier/sync_invalidation_listener.cc
@@ -205,7 +205,7 @@ void SyncInvalidationListener::Invalidate(
 
   ObjectIdSet ids;
   ids.insert(id);
-  PrepareInvalidation(ids, payload, client, ack_handle);
+  PrepareInvalidation(ids, invalidation.version(), payload, client, ack_handle);
 }
 
 void SyncInvalidationListener::InvalidateUnknownVersion(
@@ -218,7 +218,12 @@ void SyncInvalidationListener::InvalidateUnknownVersion(
 
   ObjectIdSet ids;
   ids.insert(object_id);
-  PrepareInvalidation(ids, std::string(), client, ack_handle);
+  PrepareInvalidation(
+      ids,
+      Invalidation::kUnknownVersion,
+      std::string(),
+      client,
+      ack_handle);
 }
 
 // This should behave as if we got an invalidation with version
@@ -230,11 +235,17 @@ void SyncInvalidationListener::InvalidateAll(
   DCHECK_EQ(client, invalidation_client_.get());
   DVLOG(1) << "InvalidateAll";
 
-  PrepareInvalidation(registered_ids_, std::string(), client, ack_handle);
+  PrepareInvalidation(
+      registered_ids_,
+      Invalidation::kUnknownVersion,
+      std::string(),
+      client,
+      ack_handle);
 }
 
 void SyncInvalidationListener::PrepareInvalidation(
     const ObjectIdSet& ids,
+    int64 version,
     const std::string& payload,
     invalidation::InvalidationClient* client,
     const invalidation::AckHandle& ack_handle) {
@@ -250,6 +261,7 @@ void SyncInvalidationListener::PrepareInvalidation(
       base::Bind(&SyncInvalidationListener::EmitInvalidation,
                  weak_ptr_factory_.GetWeakPtr(),
                  ids,
+                 version,
                  payload,
                  client,
                  ack_handle));
@@ -257,13 +269,14 @@ void SyncInvalidationListener::PrepareInvalidation(
 
 void SyncInvalidationListener::EmitInvalidation(
     const ObjectIdSet& ids,
+    int64 version,
     const std::string& payload,
     invalidation::InvalidationClient* client,
     const invalidation::AckHandle& ack_handle,
     const AckHandleMap& local_ack_handles) {
   DCHECK(CalledOnValidThread());
   ObjectIdInvalidationMap invalidation_map =
-      ObjectIdSetToInvalidationMap(ids, payload);
+      ObjectIdSetToInvalidationMap(ids, version, payload);
   for (AckHandleMap::const_iterator it = local_ack_handles.begin();
        it != local_ack_handles.end(); ++it) {
     // Update in-memory copy of the invalidation state.
@@ -280,6 +293,7 @@ void SyncInvalidationListener::OnTimeout(const ObjectIdSet& ids) {
   for (ObjectIdSet::const_iterator it = ids.begin(); it != ids.end(); ++it) {
     Invalidation invalidation;
     invalidation.ack_handle = invalidation_state_map_[*it].expected;
+    invalidation.version = invalidation_state_map_[*it].version;
     invalidation.payload = invalidation_state_map_[*it].payload;
     invalidation_map.insert(std::make_pair(*it, invalidation));
   }
diff --git a/sync/notifier/sync_invalidation_listener.h b/sync/notifier/sync_invalidation_listener.h
index 3613551460..d280e2e5c6 100644
--- a/sync/notifier/sync_invalidation_listener.h
+++ b/sync/notifier/sync_invalidation_listener.h
@@ -151,10 +151,12 @@ class SYNC_EXPORT_PRIVATE SyncInvalidationListener
   void EmitStateChange();
 
   void PrepareInvalidation(const ObjectIdSet& ids,
+                           int64 version,
                            const std::string& payload,
                            invalidation::InvalidationClient* client,
                            const invalidation::AckHandle& ack_handle);
   void EmitInvalidation(const ObjectIdSet& ids,
+                        int64 version,
                         const std::string& payload,
                         invalidation::InvalidationClient* client,
                         const invalidation::AckHandle& ack_handle,
diff --git a/sync/notifier/sync_invalidation_listener_unittest.cc b/sync/notifier/sync_invalidation_listener_unittest.cc
index 3dee40cd08..d3aa712b7d 100644
--- a/sync/notifier/sync_invalidation_listener_unittest.cc
+++ b/sync/notifier/sync_invalidation_listener_unittest.cc
@@ -146,6 +146,11 @@ class FakeDelegate : public SyncInvalidationListener::Delegate {
     return (it == invalidation_counts_.end()) ? 0 : it->second;
   }
 
+  int64 GetVersion(const ObjectId& id) const {
+    ObjectIdInvalidationMap::const_iterator it = invalidations_.find(id);
+    return (it == invalidations_.end()) ? 0 : it->second.version;
+  }
+
   std::string GetPayload(const ObjectId& id) const {
     ObjectIdInvalidationMap::const_iterator it = invalidations_.find(id);
     return (it == invalidations_.end()) ? std::string() : it->second.payload;
@@ -295,6 +300,10 @@ class SyncInvalidationListenerTest : public testing::Test {
     return fake_delegate_.GetInvalidationCount(id);
   }
 
+  int64 GetVersion(const ObjectId& id) const {
+    return fake_delegate_.GetVersion(id);
+  }
+
   std::string GetPayload(const ObjectId& id) const {
     return fake_delegate_.GetPayload(id);
   }
@@ -437,6 +446,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateNoPayload) {
   FireInvalidate(id, kVersion1, NULL);
 
   EXPECT_EQ(1, GetInvalidationCount(id));
+  EXPECT_EQ(kVersion1, GetVersion(id));
   EXPECT_EQ("", GetPayload(id));
   EXPECT_EQ(kVersion1, GetMaxVersion(id));
   AcknowledgeAndVerify(id);
@@ -451,6 +461,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateEmptyPayload) {
   FireInvalidate(id, kVersion1, "");
 
   EXPECT_EQ(1, GetInvalidationCount(id));
+  EXPECT_EQ(kVersion1, GetVersion(id));
   EXPECT_EQ("", GetPayload(id));
   EXPECT_EQ(kVersion1, GetMaxVersion(id));
   AcknowledgeAndVerify(id);
@@ -464,6 +475,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateWithPayload) {
   FireInvalidate(id, kVersion1, kPayload1);
 
   EXPECT_EQ(1, GetInvalidationCount(id));
+  EXPECT_EQ(kVersion1, GetVersion(id));
   EXPECT_EQ(kPayload1, GetPayload(id));
   EXPECT_EQ(kVersion1, GetMaxVersion(id));
   AcknowledgeAndVerify(id);
@@ -483,6 +495,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateUnregisteredWithPayload) {
   FireInvalidate(id, kVersion1, "unregistered payload");
 
   EXPECT_EQ(1, GetInvalidationCount(id));
+  EXPECT_EQ(kVersion1, GetVersion(id));
   EXPECT_EQ("unregistered payload", GetPayload(id));
   EXPECT_EQ(kVersion1, GetMaxVersion(id));
   AcknowledgeAndVerify(id);
@@ -497,6 +510,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateVersion) {
   FireInvalidate(id, kVersion2, kPayload2);
 
   EXPECT_EQ(1, GetInvalidationCount(id));
+  EXPECT_EQ(kVersion2, GetVersion(id));
   EXPECT_EQ(kPayload2, GetPayload(id));
   EXPECT_EQ(kVersion2, GetMaxVersion(id));
   AcknowledgeAndVerify(id);
@@ -504,6 +518,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateVersion) {
   FireInvalidate(id, kVersion1, kPayload1);
 
   EXPECT_EQ(1, GetInvalidationCount(id));
+  EXPECT_EQ(kVersion2, GetVersion(id));
   EXPECT_EQ(kPayload2, GetPayload(id));
   EXPECT_EQ(kVersion2, GetMaxVersion(id));
   VerifyAcknowledged(id);
@@ -518,6 +533,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateUnknownVersion) {
   FireInvalidateUnknownVersion(id);
 
   EXPECT_EQ(1, GetInvalidationCount(id));
+  EXPECT_EQ(Invalidation::kUnknownVersion, GetVersion(id));
   EXPECT_EQ("", GetPayload(id));
   EXPECT_EQ(kMinVersion, GetMaxVersion(id));
   AcknowledgeAndVerify(id);
@@ -525,6 +541,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateUnknownVersion) {
   FireInvalidateUnknownVersion(id);
 
   EXPECT_EQ(2, GetInvalidationCount(id));
+  EXPECT_EQ(Invalidation::kUnknownVersion, GetVersion(id));
   EXPECT_EQ("", GetPayload(id));
   EXPECT_EQ(kMinVersion, GetMaxVersion(id));
   AcknowledgeAndVerify(id);
@@ -538,6 +555,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateAll) {
   for (ObjectIdSet::const_iterator it = registered_ids_.begin();
        it != registered_ids_.end(); ++it) {
     EXPECT_EQ(1, GetInvalidationCount(*it));
+    EXPECT_EQ(Invalidation::kUnknownVersion, GetVersion(*it));
     EXPECT_EQ("", GetPayload(*it));
     EXPECT_EQ(kMinVersion, GetMaxVersion(*it));
     AcknowledgeAndVerify(*it);
@@ -549,6 +567,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateMultipleIds) {
   FireInvalidate(kBookmarksId_, 3, NULL);
 
   EXPECT_EQ(1, GetInvalidationCount(kBookmarksId_));
+  EXPECT_EQ(3, GetVersion(kBookmarksId_));
   EXPECT_EQ("", GetPayload(kBookmarksId_));
   EXPECT_EQ(3, GetMaxVersion(kBookmarksId_));
   AcknowledgeAndVerify(kBookmarksId_);
@@ -556,6 +575,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateMultipleIds) {
   FireInvalidate(kExtensionsId_, 2, NULL);
 
   EXPECT_EQ(1, GetInvalidationCount(kExtensionsId_));
+  EXPECT_EQ(2, GetVersion(kExtensionsId_));
   EXPECT_EQ("", GetPayload(kExtensionsId_));
   EXPECT_EQ(2, GetMaxVersion(kExtensionsId_));
   AcknowledgeAndVerify(kExtensionsId_);
@@ -565,12 +585,14 @@ TEST_F(SyncInvalidationListenerTest, InvalidateMultipleIds) {
   FireInvalidate(kBookmarksId_, 1, NULL);
 
   EXPECT_EQ(1, GetInvalidationCount(kBookmarksId_));
+  EXPECT_EQ(3, GetVersion(kBookmarksId_));
   EXPECT_EQ("", GetPayload(kBookmarksId_));
   EXPECT_EQ(3, GetMaxVersion(kBookmarksId_));
 
   FireInvalidate(kExtensionsId_, 1, NULL);
 
   EXPECT_EQ(1, GetInvalidationCount(kExtensionsId_));
+  EXPECT_EQ(2, GetVersion(kExtensionsId_));
   EXPECT_EQ("", GetPayload(kExtensionsId_));
   EXPECT_EQ(2, GetMaxVersion(kExtensionsId_));
 
@@ -579,11 +601,13 @@ TEST_F(SyncInvalidationListenerTest, InvalidateMultipleIds) {
   FireInvalidateAll();
 
   EXPECT_EQ(2, GetInvalidationCount(kBookmarksId_));
+  EXPECT_EQ(Invalidation::kUnknownVersion, GetVersion(kBookmarksId_));
   EXPECT_EQ("", GetPayload(kBookmarksId_));
   EXPECT_EQ(3, GetMaxVersion(kBookmarksId_));
   AcknowledgeAndVerify(kBookmarksId_);
 
   EXPECT_EQ(1, GetInvalidationCount(kPreferencesId_));
+  EXPECT_EQ(Invalidation::kUnknownVersion, GetVersion(kPreferencesId_));
   EXPECT_EQ("", GetPayload(kPreferencesId_));
   EXPECT_EQ(kMinVersion, GetMaxVersion(kPreferencesId_));
   AcknowledgeAndVerify(kPreferencesId_);
@@ -591,6 +615,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateMultipleIds) {
   // Note that kExtensionsId_ is not registered, so InvalidateAll() shouldn't
   // affect it.
   EXPECT_EQ(1, GetInvalidationCount(kExtensionsId_));
+  EXPECT_EQ(2, GetVersion(kExtensionsId_));
   EXPECT_EQ("", GetPayload(kExtensionsId_));
   EXPECT_EQ(2, GetMaxVersion(kExtensionsId_));
   VerifyAcknowledged(kExtensionsId_);
@@ -599,18 +624,21 @@ TEST_F(SyncInvalidationListenerTest, InvalidateMultipleIds) {
 
   FireInvalidate(kPreferencesId_, 5, NULL);
   EXPECT_EQ(2, GetInvalidationCount(kPreferencesId_));
+  EXPECT_EQ(5, GetVersion(kPreferencesId_));
   EXPECT_EQ("", GetPayload(kPreferencesId_));
   EXPECT_EQ(5, GetMaxVersion(kPreferencesId_));
   AcknowledgeAndVerify(kPreferencesId_);
 
   FireInvalidate(kExtensionsId_, 3, NULL);
   EXPECT_EQ(2, GetInvalidationCount(kExtensionsId_));
+  EXPECT_EQ(3, GetVersion(kExtensionsId_));
   EXPECT_EQ("", GetPayload(kExtensionsId_));
   EXPECT_EQ(3, GetMaxVersion(kExtensionsId_));
   AcknowledgeAndVerify(kExtensionsId_);
 
   FireInvalidate(kBookmarksId_, 4, NULL);
   EXPECT_EQ(3, GetInvalidationCount(kBookmarksId_));
+  EXPECT_EQ(4, GetVersion(kBookmarksId_));
   EXPECT_EQ("", GetPayload(kBookmarksId_));
   EXPECT_EQ(4, GetMaxVersion(kBookmarksId_));
   AcknowledgeAndVerify(kBookmarksId_);
@@ -628,6 +656,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateOneTimeout) {
   // Trigger the initial invalidation.
   FireInvalidate(kBookmarksId_, 3, NULL);
   EXPECT_EQ(1, GetInvalidationCount(kBookmarksId_));
+  EXPECT_EQ(3, GetVersion(kBookmarksId_));
   EXPECT_EQ("", GetPayload(kBookmarksId_));
   EXPECT_EQ(3, GetMaxVersion(kBookmarksId_));
   VerifyUnacknowledged(kBookmarksId_);
@@ -638,6 +667,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidateOneTimeout) {
       tick_clock_.NowTicks()));
   EXPECT_EQ(2, GetInvalidationCount(kBookmarksId_));
   // Other properties should remain the same.
+  EXPECT_EQ(3, GetVersion(kBookmarksId_));
   EXPECT_EQ("", GetPayload(kBookmarksId_));
   EXPECT_EQ(3, GetMaxVersion(kBookmarksId_));
 
@@ -655,6 +685,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidationTimeoutRestart) {
 
   FireInvalidate(kBookmarksId_, 3, NULL);
   EXPECT_EQ(1, GetInvalidationCount(kBookmarksId_));
+  EXPECT_EQ(3, GetVersion(kBookmarksId_));
   EXPECT_EQ("", GetPayload(kBookmarksId_));
   EXPECT_EQ(3, GetMaxVersion(kBookmarksId_));
 
@@ -664,6 +695,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidationTimeoutRestart) {
       tick_clock_.NowTicks()));
   EXPECT_EQ(2, GetInvalidationCount(kBookmarksId_));
   // Other properties should remain the same.
+  EXPECT_EQ(3, GetVersion(kBookmarksId_));
   EXPECT_EQ("", GetPayload(kBookmarksId_));
   EXPECT_EQ(3, GetMaxVersion(kBookmarksId_));
 
@@ -676,6 +708,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidationTimeoutRestart) {
 
   // The bookmark invalidation state should not have changed.
   EXPECT_EQ(2, GetInvalidationCount(kBookmarksId_));
+  EXPECT_EQ(3, GetVersion(kBookmarksId_));
   EXPECT_EQ("", GetPayload(kBookmarksId_));
   EXPECT_EQ(3, GetMaxVersion(kBookmarksId_));
 
@@ -685,6 +718,7 @@ TEST_F(SyncInvalidationListenerTest, InvalidationTimeoutRestart) {
       tick_clock_.NowTicks()));
   EXPECT_EQ(3, GetInvalidationCount(kBookmarksId_));
   // Other properties should remain the same.
+  EXPECT_EQ(3, GetVersion(kBookmarksId_));
   EXPECT_EQ("", GetPayload(kBookmarksId_));
   EXPECT_EQ(3, GetMaxVersion(kBookmarksId_));
 
diff --git a/sync/protocol/experiments_specifics.proto b/sync/protocol/experiments_specifics.proto
index f834cb91c0..1e8732fd02 100644
--- a/sync/protocol/experiments_specifics.proto
+++ b/sync/protocol/experiments_specifics.proto
@@ -34,6 +34,11 @@ message FaviconSyncFlags {
   optional int32 favicon_sync_limit = 2 [default = 200];
 }
 
+// Flags for enabling the experimental no-precommit GU feature.
+message PreCommitUpdateAvoidanceFlags {
+  optional bool enabled = 1;
+}
+
 // Contains one flag or set of related flags.  Each node of the experiments type
 // will have a unique_client_tag identifying which flags it contains.  By
 // convention, the tag name should match the sub-message name.
@@ -42,4 +47,5 @@ message ExperimentsSpecifics {
   optional HistoryDeleteDirectives history_delete_directives = 2;
   optional AutofillCullingFlags autofill_culling = 3;
   optional FaviconSyncFlags favicon_sync = 4;
+  optional PreCommitUpdateAvoidanceFlags pre_commit_update_avoidance = 5;
 }
diff --git a/sync/protocol/proto_value_conversions.cc b/sync/protocol/proto_value_conversions.cc
index f0a2011c27..9ccc5eb0c8 100644
--- a/sync/protocol/proto_value_conversions.cc
+++ b/sync/protocol/proto_value_conversions.cc
@@ -352,6 +352,7 @@ base::DictionaryValue* ExperimentsSpecificsToValue(
   SET_EXPERIMENT_ENABLED_FIELD(keystore_encryption);
   SET_EXPERIMENT_ENABLED_FIELD(history_delete_directives);
   SET_EXPERIMENT_ENABLED_FIELD(autofill_culling);
+  SET_EXPERIMENT_ENABLED_FIELD(pre_commit_update_avoidance);
   if (proto.has_favicon_sync())
     SET(favicon_sync, FaviconSyncFlagsToValue);
   return value;
diff --git a/sync/sessions/data_type_tracker.cc b/sync/sessions/data_type_tracker.cc
index 3eabbbe758..a061679839 100644
--- a/sync/sessions/data_type_tracker.cc
+++ b/sync/sessions/data_type_tracker.cc
@@ -59,7 +59,17 @@ bool DataTypeTracker::IsSyncRequired() const {
   return !IsThrottled() &&
       (local_nudge_count_ > 0 ||
        local_refresh_request_count_ > 0 ||
-       !pending_payloads_.empty());
+       HasPendingInvalidation() ||
+       local_payload_overflow_ ||
+       server_payload_overflow_);
+}
+
+bool DataTypeTracker::IsGetUpdatesRequired() const {
+  return !IsThrottled() &&
+      (local_refresh_request_count_ > 0 ||
+       HasPendingInvalidation() ||
+       local_payload_overflow_ ||
+       server_payload_overflow_);
 }
 
 bool DataTypeTracker::HasLocalChangePending() const {
diff --git a/sync/sessions/data_type_tracker.h b/sync/sessions/data_type_tracker.h
index 6488f8e105..30bc3b6dbb 100644
--- a/sync/sessions/data_type_tracker.h
+++ b/sync/sessions/data_type_tracker.h
@@ -49,6 +49,10 @@ class DataTypeTracker {
   // cycle.  That's for the scheduler to decide.
   bool IsSyncRequired() const;
 
+  // Returns true if there is a good reason to fetch updates for this type as
+  // part of the next sync cycle.
+  bool IsGetUpdatesRequired() const;
+
   // Returns true if there is an uncommitted local change.
   bool HasLocalChangePending() const;
 
diff --git a/sync/sessions/nudge_tracker.cc b/sync/sessions/nudge_tracker.cc
index 144860b1a8..f9b90386f5 100644
--- a/sync/sessions/nudge_tracker.cc
+++ b/sync/sessions/nudge_tracker.cc
@@ -38,6 +38,16 @@ bool NudgeTracker::IsSyncRequired() const {
   return false;
 }
 
+bool NudgeTracker::IsGetUpdatesRequired() const {
+  for (TypeTrackerMap::const_iterator it = type_trackers_.begin();
+       it != type_trackers_.end(); ++it) {
+    if (it->second.IsGetUpdatesRequired()) {
+      return true;
+    }
+  }
+  return false;
+}
+
 void NudgeTracker::RecordSuccessfulSyncCycle() {
   updates_source_ = sync_pb::GetUpdatesCallerInfo::UNKNOWN;
 
diff --git a/sync/sessions/nudge_tracker.h b/sync/sessions/nudge_tracker.h
index 0e8ab51202..f8109a42d3 100644
--- a/sync/sessions/nudge_tracker.h
+++ b/sync/sessions/nudge_tracker.h
@@ -34,6 +34,10 @@ class SYNC_EXPORT_PRIVATE NudgeTracker {
   // perform a sync cycle; that's the scheduler's job.
   bool IsSyncRequired() const;
 
+  // Returns true if there is a good reason for performing a get updates
+  // request as part of the next sync cycle.
+  bool IsGetUpdatesRequired() const;
+
   // Tells this class that all required update fetching and committing has
   // completed successfully.
   void RecordSuccessfulSyncCycle();
diff --git a/sync/sessions/nudge_tracker_unittest.cc b/sync/sessions/nudge_tracker_unittest.cc
index 8439af1d82..598a3e6b43 100644
--- a/sync/sessions/nudge_tracker_unittest.cc
+++ b/sync/sessions/nudge_tracker_unittest.cc
@@ -61,6 +61,7 @@ TEST_F(NudgeTrackerTest, EmptyNudgeTracker) {
   NudgeTracker nudge_tracker;
 
   EXPECT_FALSE(nudge_tracker.IsSyncRequired());
+  EXPECT_FALSE(nudge_tracker.IsGetUpdatesRequired());
   EXPECT_EQ(sync_pb::GetUpdatesCallerInfo::UNKNOWN,
             nudge_tracker.updates_source());
 
@@ -300,6 +301,33 @@ TEST_F(NudgeTrackerTest, IsSyncRequired) {
   EXPECT_FALSE(nudge_tracker.IsSyncRequired());
 }
 
+// Basic tests for the IsGetUpdatesRequired() flag.
+TEST_F(NudgeTrackerTest, IsGetUpdatesRequired) {
+  NudgeTracker nudge_tracker;
+  EXPECT_FALSE(nudge_tracker.IsGetUpdatesRequired());
+
+  // Local changes.
+  nudge_tracker.RecordLocalChange(ModelTypeSet(SESSIONS));
+  EXPECT_FALSE(nudge_tracker.IsGetUpdatesRequired());
+  nudge_tracker.RecordSuccessfulSyncCycle();
+  EXPECT_FALSE(nudge_tracker.IsGetUpdatesRequired());
+
+  // Refresh requests.
+  nudge_tracker.RecordLocalRefreshRequest(ModelTypeSet(SESSIONS));
+  EXPECT_TRUE(nudge_tracker.IsGetUpdatesRequired());
+  nudge_tracker.RecordSuccessfulSyncCycle();
+  EXPECT_FALSE(nudge_tracker.IsGetUpdatesRequired());
+
+  // Invalidations.
+  ModelTypeInvalidationMap invalidation_map =
+      ModelTypeSetToInvalidationMap(ModelTypeSet(PREFERENCES),
+                                    std::string("hint"));
+  nudge_tracker.RecordRemoteInvalidation(invalidation_map);
+  EXPECT_TRUE(nudge_tracker.IsGetUpdatesRequired());
+  nudge_tracker.RecordSuccessfulSyncCycle();
+  EXPECT_FALSE(nudge_tracker.IsGetUpdatesRequired());
+}
+
 // Test IsSyncRequired() responds correctly to data type throttling.
 TEST_F(NudgeTrackerTest, IsSyncRequired_Throttling) {
   NudgeTracker nudge_tracker;
@@ -320,7 +348,7 @@ TEST_F(NudgeTrackerTest, IsSyncRequired_Throttling) {
   EXPECT_FALSE(nudge_tracker.IsSyncRequired());
 
   // A refresh request for bookmarks means we have reason to sync again.
-  nudge_tracker.RecordLocalChange(ModelTypeSet(BOOKMARKS));
+  nudge_tracker.RecordLocalRefreshRequest(ModelTypeSet(BOOKMARKS));
   EXPECT_TRUE(nudge_tracker.IsSyncRequired());
 
   // A successful sync cycle means we took care of bookmarks.
@@ -335,6 +363,41 @@ TEST_F(NudgeTrackerTest, IsSyncRequired_Throttling) {
   EXPECT_TRUE(nudge_tracker.IsSyncRequired());
 }
 
+// Test IsGetUpdatesRequired() responds correctly to data type throttling.
+TEST_F(NudgeTrackerTest, IsGetUpdatesRequired_Throttling) {
+  NudgeTracker nudge_tracker;
+  const base::TimeTicks t0 = base::TimeTicks::FromInternalValue(1234);
+  const base::TimeDelta throttle_length = base::TimeDelta::FromMinutes(10);
+  const base::TimeTicks t1 = t0 + throttle_length;
+
+  EXPECT_FALSE(nudge_tracker.IsGetUpdatesRequired());
+
+  // A refresh request to sessions enables the flag.
+  nudge_tracker.RecordLocalRefreshRequest(ModelTypeSet(SESSIONS));
+  EXPECT_TRUE(nudge_tracker.IsGetUpdatesRequired());
+
+  // But the throttling of sessions unsets it.
+  nudge_tracker.SetTypesThrottledUntil(ModelTypeSet(SESSIONS),
+                                       throttle_length,
+                                       t0);
+  EXPECT_FALSE(nudge_tracker.IsGetUpdatesRequired());
+
+  // A refresh request for bookmarks means we have reason to sync again.
+  nudge_tracker.RecordLocalRefreshRequest(ModelTypeSet(BOOKMARKS));
+  EXPECT_TRUE(nudge_tracker.IsGetUpdatesRequired());
+
+  // A successful sync cycle means we took care of bookmarks.
+  nudge_tracker.RecordSuccessfulSyncCycle();
+  EXPECT_FALSE(nudge_tracker.IsGetUpdatesRequired());
+
+  // But we still haven't dealt with sessions.  We'll need to remember
+  // that sessions are out of sync and re-enable the flag when their
+  // throttling interval expires.
+  nudge_tracker.UpdateTypeThrottlingState(t1);
+  EXPECT_FALSE(nudge_tracker.IsTypeThrottled(SESSIONS));
+  EXPECT_TRUE(nudge_tracker.IsGetUpdatesRequired());
+}
+
 // Tests throttling-related getter functions when no types are throttled.
 TEST_F(NudgeTrackerTest, NoTypesThrottled) {
   NudgeTracker nudge_tracker;
diff --git a/sync/sessions/sync_session_context.cc b/sync/sessions/sync_session_context.cc
index 9043db3cba..c48c32b31e 100644
--- a/sync/sessions/sync_session_context.cc
+++ b/sync/sessions/sync_session_context.cc
@@ -22,6 +22,7 @@ SyncSessionContext::SyncSessionContext(
     DebugInfoGetter* debug_info_getter,
     TrafficRecorder* traffic_recorder,
     bool keystore_encryption_enabled,
+    bool client_enabled_pre_commit_update_avoidance,
     const std::string& invalidator_client_id)
     : connection_manager_(connection_manager),
       directory_(directory),
@@ -31,7 +32,10 @@ SyncSessionContext::SyncSessionContext(
       debug_info_getter_(debug_info_getter),
       traffic_recorder_(traffic_recorder),
       keystore_encryption_enabled_(keystore_encryption_enabled),
-      invalidator_client_id_(invalidator_client_id) {
+      invalidator_client_id_(invalidator_client_id),
+      server_enabled_pre_commit_update_avoidance_(false),
+      client_enabled_pre_commit_update_avoidance_(
+          client_enabled_pre_commit_update_avoidance) {
   for (size_t i = 0u; i < workers.size(); ++i)
     workers_.push_back(workers[i]);
 
diff --git a/sync/sessions/sync_session_context.h b/sync/sessions/sync_session_context.h
index b694162c15..76170958ec 100644
--- a/sync/sessions/sync_session_context.h
+++ b/sync/sessions/sync_session_context.h
@@ -55,6 +55,7 @@ class SYNC_EXPORT_PRIVATE SyncSessionContext {
                      DebugInfoGetter* debug_info_getter,
                      TrafficRecorder* traffic_recorder,
                      bool keystore_encryption_enabled,
+                     bool client_enabled_pre_commit_update_avoidance,
                      const std::string& invalidator_client_id);
 
   ~SyncSessionContext();
@@ -129,6 +130,15 @@ class SYNC_EXPORT_PRIVATE SyncSessionContext {
     return invalidator_client_id_;
   }
 
+  bool ShouldFetchUpdatesBeforeCommit() const {
+    return !(server_enabled_pre_commit_update_avoidance_ ||
+             client_enabled_pre_commit_update_avoidance_);
+  }
+
+  void set_server_enabled_pre_commit_update_avoidance(bool value) {
+    server_enabled_pre_commit_update_avoidance_ = value;
+  }
+
  private:
   // Rather than force clients to set and null-out various context members, we
   // extend our encapsulation boundary to scoped helpers that take care of this
@@ -181,6 +191,15 @@ class SYNC_EXPORT_PRIVATE SyncSessionContext {
   // prevent us from receiving notifications of changes we make ourselves.
   const std::string invalidator_client_id_;
 
+  // Flag to enable or disable the no pre-commit GetUpdates experiment.  When
+  // this flag is set to false, the syncer has the option of not performing at
+  // GetUpdates request when there is nothing to fetch.
+  bool server_enabled_pre_commit_update_avoidance_;
+
+  // If true, indicates that we've been passed a command-line flag to force
+  // enable the pre-commit update avoidance experiment described above.
+  const bool client_enabled_pre_commit_update_avoidance_;
+
   DISALLOW_COPY_AND_ASSIGN(SyncSessionContext);
 };
 
diff --git a/sync/sessions/sync_session_unittest.cc b/sync/sessions/sync_session_unittest.cc
index c98b63923f..4acee569fe 100644
--- a/sync/sessions/sync_session_unittest.cc
+++ b/sync/sessions/sync_session_unittest.cc
@@ -65,6 +65,7 @@ class SyncSessionTest : public testing::Test,
             NULL,
             NULL,
             true,  // enable keystore encryption
+            false,  // force enable pre-commit GU avoidance experiment
             "fake_invalidator_client_id"));
     context_->set_routing_info(routes_);
 
diff --git a/sync/syncable/model_type.cc b/sync/syncable/model_type.cc
index 5e227948b7..b9dacbecf1 100644
--- a/sync/syncable/model_type.cc
+++ b/sync/syncable/model_type.cc
@@ -367,7 +367,7 @@ ModelTypeSet EncryptableUserTypes() {
   encryptable_user_types.Remove(SYNCED_NOTIFICATIONS);
   // Priority preferences are not encrypted because they might be synced before
   // encryption is ready.
-  encryptable_user_types.RemoveAll(PriorityUserTypes());
+  encryptable_user_types.Remove(PRIORITY_PREFERENCES);
   // Managed user settings are not encrypted since they are set server-side.
   encryptable_user_types.Remove(MANAGED_USER_SETTINGS);
   // Managed users are not encrypted since they are managed server-side.
@@ -380,7 +380,7 @@ ModelTypeSet EncryptableUserTypes() {
 }
 
 ModelTypeSet PriorityUserTypes() {
-  return ModelTypeSet(PRIORITY_PREFERENCES, MANAGED_USERS);
+  return ModelTypeSet(PRIORITY_PREFERENCES);
 }
 
 ModelTypeSet ControlTypes() {
@@ -405,6 +405,26 @@ bool IsControlType(ModelType model_type) {
   return ControlTypes().Has(model_type);
 }
 
+ModelTypeSet CoreTypes() {
+  syncer::ModelTypeSet result;
+  result.PutAll(PriorityCoreTypes());
+
+  // The following are low priority core types.
+  result.Put(SYNCED_NOTIFICATIONS);
+
+  return result;
+}
+
+ModelTypeSet PriorityCoreTypes() {
+  syncer::ModelTypeSet result;
+  result.PutAll(ControlTypes());
+
+  // The following are non-control core types.
+  result.Put(MANAGED_USERS);
+
+  return result;
+}
+
 const char* ModelTypeToString(ModelType model_type) {
   // This is used in serialization routines as well as for displaying debug
   // information.  Do not attempt to change these string values unless you know
diff --git a/sync/test/android/javatests/src/org/chromium/sync/test/util/MockAccountManager.java b/sync/test/android/javatests/src/org/chromium/sync/test/util/MockAccountManager.java
index b79abcf5d5..da16fae2ae 100644
--- a/sync/test/android/javatests/src/org/chromium/sync/test/util/MockAccountManager.java
+++ b/sync/test/android/javatests/src/org/chromium/sync/test/util/MockAccountManager.java
@@ -238,7 +238,8 @@ public class MockAccountManager implements AccountManagerDelegate {
         } else {
             Log.d(TAG, "getAuthTokenFuture: Account " + ah.getAccount() +
                     " is asking for permission for " + authTokenType);
-            final Intent intent = newGrantCredentialsPermissionIntent(true, account, authTokenType);
+            final Intent intent = newGrantCredentialsPermissionIntent(
+                    activity != null, account, authTokenType);
             return runTask(mExecutor,
                     new AccountManagerAuthTokenTask(activity, handler, callback,
                             account, authTokenType,
@@ -495,10 +496,13 @@ public class MockAccountManager implements AccountManagerDelegate {
             try {
                 Bundle bundle = mCallable.call();
                 Intent intent = bundle.getParcelable(AccountManager.KEY_INTENT);
-                if (intent != null && mActivity != null) {
-                    // Since the user provided an Activity we will silently start intents we see.
-                    // Starting activity and waiting for it to finish.
-                    waitForActivity(mActivity, intent);
+                if (intent != null) {
+                    // Start the intent activity and wait for it to finish.
+                    if (mActivity != null) {
+                        waitForActivity(mActivity, intent);
+                    } else {
+                        waitForActivity(mContext, intent);
+                    }
                     if (mAccountAuthTokenPreparation == null) {
                         throw new IllegalStateException("No account preparation ready for " +
                                 mAccount + ", authTokenType = " + mAuthTokenType +
diff --git a/sync/test/engine/syncer_command_test.h b/sync/test/engine/syncer_command_test.h
index c292fe0b96..93106b9933 100644
--- a/sync/test/engine/syncer_command_test.h
+++ b/sync/test/engine/syncer_command_test.h
@@ -136,6 +136,7 @@ class SyncerCommandTestBase : public testing::Test,
             &mock_debug_info_getter_,
             &traffic_recorder_,
             true,  // enable keystore encryption
+            false,  // force enable pre-commit GU avoidance experiment
             "fake_invalidator_client_id"));
     context_->set_routing_info(routing_info_);
     context_->set_account_name(directory()->name());
diff --git a/sync/tools/testserver/chromiumsync.py b/sync/tools/testserver/chromiumsync.py
index 7aac4deeaa..834765ff71 100644
--- a/sync/tools/testserver/chromiumsync.py
+++ b/sync/tools/testserver/chromiumsync.py
@@ -129,8 +129,9 @@ UNIX_TIME_EPOCH = (1970, 1, 1, 0, 0, 0, 3, 1, 0)
 # The number of characters in the server-generated encryption key.
 KEYSTORE_KEY_LENGTH = 16
 
-# The hashed client tag for the keystore encryption experiment node.
+# The hashed client tags for some experiment nodes.
 KEYSTORE_ENCRYPTION_EXPERIMENT_TAG = "pis8ZRzh98/MKLtVEio2mr42LQA="
+PRE_COMMIT_GU_AVOIDANCE_EXPERIMENT_TAG = "Z1xgeh3QUBa50vdEPd8C/4c7jfE="
 
 class Error(Exception):
   """Error class for this module."""
@@ -1101,6 +1102,25 @@ class SyncDataModel(object):
       user.specifics.managed_user.acknowledged = True
       self._SaveEntry(user)
 
+  def TriggerEnablePreCommitGetUpdateAvoidance(self):
+    """Sets the experiment to enable pre-commit GetUpdate avoidance."""
+    experiment_id = self._ServerTagToId("google_chrome_experiments")
+    pre_commit_gu_avoidance_id = self._ClientTagToId(
+        EXPERIMENTS,
+        PRE_COMMIT_GU_AVOIDANCE_EXPERIMENT_TAG)
+    entry = self._entries.get(pre_commit_gu_avoidance_id)
+    if entry is None:
+      entry = sync_pb2.SyncEntity()
+      entry.id_string = pre_commit_gu_avoidance_id
+      entry.name = "Pre-commit GU avoidance"
+      entry.client_defined_unique_tag = PRE_COMMIT_GU_AVOIDANCE_EXPERIMENT_TAG
+      entry.folder = False
+      entry.deleted = False
+      entry.specifics.CopyFrom(GetDefaultEntitySpecifics(EXPERIMENTS))
+      self._WritePosition(entry, experiment_id)
+    entry.specifics.experiments.pre_commit_update_avoidance.enabled = True
+    self._SaveEntry(entry)
+
   def SetInducedError(self, error, error_frequency,
                       sync_count_before_errors):
     self.induced_error = error
@@ -1281,6 +1301,14 @@ class TestServer(object):
         '<html><title>Enable Managed User Acknowledgement</title>'
             '<h1>Enable Managed User Acknowledgement</h1></html>')
 
+  def HandleEnablePreCommitGetUpdateAvoidance(self):
+    """Enables the pre-commit GU avoidance experiment."""
+    self.account.TriggerEnablePreCommitGetUpdateAvoidance()
+    return (
+        200,
+        '<html><title>Enable pre-commit GU avoidance</title>'
+            '<H1>Enable pre-commit GU avoidance</H1></html>')
+
   def HandleCommand(self, query, raw_request):
     """Decode and handle a sync command from a raw input of bytes.
 
diff --git a/sync/tools/testserver/sync_testserver.py b/sync/tools/testserver/sync_testserver.py
index 4fbfdaf9ac..53532cb5b7 100755
--- a/sync/tools/testserver/sync_testserver.py
+++ b/sync/tools/testserver/sync_testserver.py
@@ -150,7 +150,8 @@ class SyncPageHandler(testserver_base.BasePageHandler):
                     self.ChromiumSyncCreateSyncedBookmarksOpHandler,
                     self.ChromiumSyncEnableKeystoreEncryptionOpHandler,
                     self.ChromiumSyncRotateKeystoreKeysOpHandler,
-                    self.ChromiumSyncEnableManagedUserAcknowledgementHandler]
+                    self.ChromiumSyncEnableManagedUserAcknowledgementHandler,
+                    self.ChromiumSyncEnablePreCommitGetUpdateAvoidanceHandler]
 
     post_handlers = [self.ChromiumSyncCommandHandler,
                      self.ChromiumSyncTimeHandler]
@@ -427,6 +428,19 @@ class SyncPageHandler(testserver_base.BasePageHandler):
     self.wfile.write(raw_reply)
     return True
 
+  def ChromiumSyncEnablePreCommitGetUpdateAvoidanceHandler(self):
+    test_name = "/chromiumsync/enableprecommitgetupdateavoidance"
+    if not self._ShouldHandleRequest(test_name):
+      return False
+    result, raw_reply = (
+        self.server._sync_handler.HandleEnablePreCommitGetUpdateAvoidance())
+    self.send_response(result)
+    self.send_header('Content-Type', 'text/html')
+    self.send_header('Content-Length', len(raw_reply))
+    self.end_headers()
+    self.wfile.write(raw_reply)
+    return True
+
 class SyncServerRunner(testserver_base.TestServerRunner):
   """TestServerRunner for the net test servers."""