Fix clang-tidy performance warnings in shill.

am: ec5aa476af

Change-Id: I6985e582b5aa76b82796e80e855b5edfbd24c7f1

43 files changed, 110 insertions, 110 deletions

diff --git a/connection_health_checker.cc b/connection_health_checker.cc
index 9291e572..7626e45e 100644
--- a/connection_health_checker.cc
+++ b/connection_health_checker.cc
@@ -127,7 +127,7 @@ bool ConnectionHealthChecker::health_check_in_progress() const {
   return health_check_in_progress_;
 }
 
-void ConnectionHealthChecker::AddRemoteIP(IPAddress ip) {
+void ConnectionHealthChecker::AddRemoteIP(const IPAddress& ip) {
   remote_ips_->AddUnique(ip);
 }
 
@@ -206,7 +206,7 @@ void ConnectionHealthChecker::Stop() {
   num_tx_queue_polling_attempts_ = 0;
 }
 
-void ConnectionHealthChecker::SetConnection(ConnectionRefPtr connection) {
+void ConnectionHealthChecker::SetConnection(const ConnectionRefPtr& connection) {
   SLOG(connection_.get(), 3) << __func__;
   connection_ = connection;
   tcp_connection_.reset(new AsyncConnection(connection_->interface_name(),
diff --git a/connection_health_checker.h b/connection_health_checker.h
index 791d7a5f..6208fa5c 100644
--- a/connection_health_checker.h
+++ b/connection_health_checker.h
@@ -77,12 +77,12 @@ class ConnectionHealthChecker {
 
   // Name resolution can fail in conditions -(1)- and -(2)-. Add an IP address
   // to attempt the TCP connection with.
-  virtual void AddRemoteIP(IPAddress ip);
+  virtual void AddRemoteIP(const IPAddress& ip);
 
   // Change the associated Connection on the Device.
   // This will restart any ongoing health check. Any ongoing DNS query will be
   // dropped (not restarted).
-  virtual void SetConnection(ConnectionRefPtr connection);
+  virtual void SetConnection(const ConnectionRefPtr& connection);
 
   // Start a connection health check. The health check involves one or more
   // attempts at establishing and using a TCP connection. |result_callback_| is
diff --git a/connection_health_checker_unittest.cc b/connection_health_checker_unittest.cc
index 3a8edaf3..09ca0596 100644
--- a/connection_health_checker_unittest.cc
+++ b/connection_health_checker_unittest.cc
@@ -256,7 +256,7 @@ class ConnectionHealthCheckerTest : public Test {
   // This only works if GetSocketInfo is called with kProxyFD.
   // If no matching sock_info is provided (Does not belong to proxy socket),
   // GetSocketInfo will (correctly) return false.
-  void ExpectGetSocketInfoReturns(SocketInfo sock_info) {
+  void ExpectGetSocketInfoReturns(const SocketInfo& sock_info) {
     vector<SocketInfo> info_list;
     info_list.push_back(sock_info);
     EXPECT_CALL(*socket_, GetSockName(kProxyFD, _, _))
diff --git a/connection_info_unittest.cc b/connection_info_unittest.cc
index c1b182d9..09634d1e 100644
--- a/connection_info_unittest.cc
+++ b/connection_info_unittest.cc
@@ -75,7 +75,7 @@ TEST_F(ConnectionInfoTest, CopyConstructor) {
                                 ByteString(kIPAddress4, sizeof(kIPAddress4))),
                       kPort4);
 
-  ConnectionInfo info_copy(info);
+  const ConnectionInfo& info_copy(info);
   ExpectConnectionInfoEqual(info, info_copy);
 }
 
@@ -96,7 +96,7 @@ TEST_F(ConnectionInfoTest, AssignmentOperator) {
                                 ByteString(kIPAddress4, sizeof(kIPAddress4))),
                       kPort4);
 
-  ConnectionInfo info_copy = info;
+  const ConnectionInfo& info_copy = info;
   ExpectConnectionInfoEqual(info, info_copy);
 }
 
diff --git a/connection_unittest.cc b/connection_unittest.cc
index db4ee3ed..7fe25568 100644
--- a/connection_unittest.cc
+++ b/connection_unittest.cc
@@ -123,7 +123,7 @@ class ConnectionTest : public Test {
     connection_ = nullptr;
   }
 
-  void ReplaceSingletons(ConnectionRefPtr connection) {
+  void ReplaceSingletons(const ConnectionRefPtr& connection) {
 #if !defined(__ANDROID__)
     connection->resolver_ = &resolver_;
 #else
@@ -141,21 +141,21 @@ class ConnectionTest : public Test {
     ip6config_->UpdateProperties(ipv6_properties_, true);
   }
 
-  bool PinHostRoute(ConnectionRefPtr connection,
-                    const IPAddress trusted_ip,
-                    const IPAddress gateway) {
+  bool PinHostRoute(const ConnectionRefPtr& connection,
+                    const IPAddress& trusted_ip,
+                    const IPAddress& gateway) {
     return connection->PinHostRoute(trusted_ip, gateway);
   }
 
-  const IPAddress& GetLocalAddress(ConnectionRefPtr connection) {
+  const IPAddress& GetLocalAddress(const ConnectionRefPtr& connection) {
     return connection->local_;
   }
 
-  const IPAddress& GetGatewayAddress(ConnectionRefPtr connection) {
+  const IPAddress& GetGatewayAddress(const ConnectionRefPtr& connection) {
     return connection->gateway_;
   }
 
-  bool GetHasBroadcastDomain(ConnectionRefPtr connection) {
+  bool GetHasBroadcastDomain(const ConnectionRefPtr& connection) {
     return connection->has_broadcast_domain_;
   }
 
diff --git a/crypto_util_proxy_unittest.cc b/crypto_util_proxy_unittest.cc
index d942f98f..8e7e3987 100644
--- a/crypto_util_proxy_unittest.cc
+++ b/crypto_util_proxy_unittest.cc
@@ -105,7 +105,7 @@ class CryptoUtilProxyTest : public testing::Test {
   pid_t HandleStartInMinijailWithPipes(
       const tracked_objects::Location& /* spawn_source */,
       const base::FilePath& /* program */,
-      vector<string> /* program_args */,
+      const vector<string>& /* program_args */,
       const std::string& /* run_as_user */,
       const std::string& /* run_as_group */,
       uint64_t /* capabilities_mask */,
diff --git a/dbus/chromeos_manager_dbus_adaptor.cc b/dbus/chromeos_manager_dbus_adaptor.cc
index 0aea07ea..0762ad6d 100644
--- a/dbus/chromeos_manager_dbus_adaptor.cc
+++ b/dbus/chromeos_manager_dbus_adaptor.cc
@@ -49,7 +49,7 @@ const char ChromeosManagerDBusAdaptor::kPath[] = "/";
 
 ChromeosManagerDBusAdaptor::ChromeosManagerDBusAdaptor(
     const scoped_refptr<dbus::Bus>& adaptor_bus,
-    const scoped_refptr<dbus::Bus> proxy_bus,
+    const scoped_refptr<dbus::Bus>& proxy_bus,
     Manager* manager)
     : org::chromium::flimflam::ManagerAdaptor(this),
       ChromeosDBusAdaptor(adaptor_bus, kPath),
diff --git a/dbus/chromeos_manager_dbus_adaptor.h b/dbus/chromeos_manager_dbus_adaptor.h
index aa6278f0..1ab4caf3 100644
--- a/dbus/chromeos_manager_dbus_adaptor.h
+++ b/dbus/chromeos_manager_dbus_adaptor.h
@@ -48,7 +48,7 @@ class ChromeosManagerDBusAdaptor
   static const char kPath[];
 
   ChromeosManagerDBusAdaptor(const scoped_refptr<dbus::Bus>& adaptor_bus,
-                             const scoped_refptr<dbus::Bus> proxy_bus,
+                             const scoped_refptr<dbus::Bus>& proxy_bus,
                              Manager* manager);
   ~ChromeosManagerDBusAdaptor() override;
 
diff --git a/dbus/dbus_service_watcher_factory.cc b/dbus/dbus_service_watcher_factory.cc
index 2493703a..3036add5 100644
--- a/dbus/dbus_service_watcher_factory.cc
+++ b/dbus/dbus_service_watcher_factory.cc
@@ -33,7 +33,7 @@ DBusServiceWatcherFactory* DBusServiceWatcherFactory::GetInstance() {
 }
 
 ChromeosDBusServiceWatcher* DBusServiceWatcherFactory::CreateDBusServiceWatcher(
-    scoped_refptr<dbus::Bus> bus, const std::string& connection_name,
+    const scoped_refptr<dbus::Bus>& bus, const std::string& connection_name,
     const base::Closure& on_connection_vanish) {
   return new ChromeosDBusServiceWatcher(bus, connection_name,
                                         on_connection_vanish);
diff --git a/dbus/dbus_service_watcher_factory.h b/dbus/dbus_service_watcher_factory.h
index f005d160..14bffe8c 100644
--- a/dbus/dbus_service_watcher_factory.h
+++ b/dbus/dbus_service_watcher_factory.h
@@ -36,7 +36,7 @@ class DBusServiceWatcherFactory {
   static DBusServiceWatcherFactory* GetInstance();
 
   virtual ChromeosDBusServiceWatcher* CreateDBusServiceWatcher(
-      scoped_refptr<dbus::Bus> bus, const std::string& connection_name,
+      const scoped_refptr<dbus::Bus>& bus, const std::string& connection_name,
       const base::Closure& on_connection_vanish);
 
  protected:
diff --git a/dbus/mock_dbus_service_watcher_factory.h b/dbus/mock_dbus_service_watcher_factory.h
index 00194f0f..ebf81265 100644
--- a/dbus/mock_dbus_service_watcher_factory.h
+++ b/dbus/mock_dbus_service_watcher_factory.h
@@ -30,7 +30,7 @@ class MockDBusServiceWatcherFactory : public DBusServiceWatcherFactory {
 
   MOCK_METHOD3(
       CreateDBusServiceWatcher,
-      ChromeosDBusServiceWatcher*(scoped_refptr<dbus::Bus> bus,
+      ChromeosDBusServiceWatcher*(const scoped_refptr<dbus::Bus>& bus,
                                   const std::string& connection_name,
                                   const base::Closure& on_connection_vanish));
 
diff --git a/device_unittest.cc b/device_unittest.cc
index 82da3fe0..e7be6f6c 100644
--- a/device_unittest.cc
+++ b/device_unittest.cc
@@ -211,11 +211,11 @@ class DeviceTest : public PropertyStoreTest {
     device_->OnIPConfigExpired(ipconfig);
   }
 
-  void SelectService(const ServiceRefPtr service) {
+  void SelectService(const ServiceRefPtr& service) {
     device_->SelectService(service);
   }
 
-  void SetConnection(ConnectionRefPtr connection) {
+  void SetConnection(const ConnectionRefPtr& connection) {
     device_->connection_ = connection;
   }
 
@@ -2666,7 +2666,7 @@ class DeviceByteCountTest : public DeviceTest {
     return true;
   }
 
-  bool ExpectByteCounts(DeviceRefPtr device,
+  bool ExpectByteCounts(const DeviceRefPtr& device,
                         int64_t expected_rx, int64_t expected_tx) {
     int64_t actual_rx = device->GetReceiveByteCount();
     int64_t actual_tx = device->GetTransmitByteCount();
@@ -2675,7 +2675,7 @@ class DeviceByteCountTest : public DeviceTest {
     return expected_rx == actual_rx && expected_tx == actual_tx;
   }
 
-  void ExpectSavedCounts(DeviceRefPtr device,
+  void ExpectSavedCounts(const DeviceRefPtr& device,
                          int64_t expected_rx, int64_t expected_tx) {
     EXPECT_CALL(storage_,
         SetUint64(_, Device::kStorageReceiveByteCount, expected_rx))
diff --git a/dhcp/dhcpv4_config.cc b/dhcp/dhcpv4_config.cc
index 1d3411f0..d62a7433 100644
--- a/dhcp/dhcpv4_config.cc
+++ b/dhcp/dhcpv4_config.cc
@@ -343,7 +343,7 @@ bool DHCPv4Config::ParseConfiguration(const KeyValueStore& configuration,
   properties->address_family = IPAddress::kFamilyIPv4;
   string classless_static_routes;
   bool default_gateway_parse_error = false;
-  for (const auto it :  configuration.properties()) {
+  for (const auto& it :  configuration.properties()) {
     const string& key = it.first;
     const brillo::Any& value = it.second;
     SLOG(nullptr, 2) << "Processing key: " << key;
diff --git a/dhcp/dhcpv4_config_unittest.cc b/dhcp/dhcpv4_config_unittest.cc
index ebe607a9..7ac534af 100644
--- a/dhcp/dhcpv4_config_unittest.cc
+++ b/dhcp/dhcpv4_config_unittest.cc
@@ -93,7 +93,7 @@ class DHCPv4ConfigTest : public PropertyStoreTest {
     config_->process_manager_ = &process_manager_;
   }
 
-  bool StartInstance(DHCPv4ConfigRefPtr config) {
+  bool StartInstance(const DHCPv4ConfigRefPtr& config) {
     return config->Start();
   }
 
@@ -109,7 +109,7 @@ class DHCPv4ConfigTest : public PropertyStoreTest {
                                          const string& vendorclass,
                                          const string& lease_suffix,
                                          bool arp_gateway);
-  void StopRunningConfigAndExpect(DHCPv4ConfigRefPtr config,
+  void StopRunningConfigAndExpect(const DHCPv4ConfigRefPtr& config,
                                   bool lease_file_exists);
 
  protected:
@@ -222,7 +222,7 @@ DHCPv4ConfigRefPtr DHCPv4ConfigTest::CreateRunningConfig(
   return config;
 }
 
-void DHCPv4ConfigTest::StopRunningConfigAndExpect(DHCPv4ConfigRefPtr config,
+void DHCPv4ConfigTest::StopRunningConfigAndExpect(const DHCPv4ConfigRefPtr& config,
                                                   bool lease_file_exists) {
   ScopedMockLog log;
   // We use a non-zero exit status so that we get the log message.
diff --git a/manager.cc b/manager.cc
index 9ff3d4e5..fb77e189 100644
--- a/manager.cc
+++ b/manager.cc
@@ -1662,8 +1662,8 @@ void Manager::VerifyAndEncryptCredentials(const string& certificate,
 }
 #endif  // DISABLE_WIFI
 
-int Manager::CalcConnectionId(std::string gateway_ip,
-                              std::string gateway_mac) {
+int Manager::CalcConnectionId(const std::string& gateway_ip,
+                              const std::string& gateway_mac) {
   return static_cast<int>(std::hash<std::string>()(gateway_ip + gateway_mac +
       std::to_string(props_.connection_id_salt)));
 }
@@ -2532,8 +2532,8 @@ ServiceRefPtr Manager::ConfigureServiceForProfile(
   return nullptr;
 }
 
-void Manager::SetupServiceInProfile(ServiceRefPtr service,
-                                    ProfileRefPtr profile,
+void Manager::SetupServiceInProfile(const ServiceRefPtr& service,
+                                    const ProfileRefPtr& profile,
                                     const KeyValueStore& args,
                                     Error* error) {
   service->SetProfile(profile);
@@ -2672,7 +2672,7 @@ void Manager::UpdateProviderMapping() {
 #endif  // DISABLE_WIMAX
 }
 
-DeviceRefPtr Manager::GetDeviceConnectedToService(ServiceRefPtr service) {
+DeviceRefPtr Manager::GetDeviceConnectedToService(const ServiceRefPtr& service) {
   for (DeviceRefPtr device : devices_) {
     if (device->IsConnectedToService(service)) {
       return device;
diff --git a/manager.h b/manager.h
index 1415c886..4b6f262e 100644
--- a/manager.h
+++ b/manager.h
@@ -505,7 +505,7 @@ class Manager : public base::SupportsWeakPtr<Manager> {
 
   // Calculate connection identifier, which is hash of salt value, gateway IP
   // address, and gateway MAC address.
-  int CalcConnectionId(std::string gateway_ip, std::string gateway_mac);
+  int CalcConnectionId(const std::string& gateway_ip, const std::string& gateway_mac);
 
   // Report the number of services associated with given connection
   // |connection_id|.
@@ -734,8 +734,8 @@ class Manager : public base::SupportsWeakPtr<Manager> {
   // the resulting configuration to |profile|.  This method is useful
   // when copying a service configuration from one profile to another,
   // or writing a newly created service config to a specific profile.
-  static void SetupServiceInProfile(ServiceRefPtr service,
-                                    ProfileRefPtr profile,
+  static void SetupServiceInProfile(const ServiceRefPtr& service,
+                                    const ProfileRefPtr& profile,
                                     const KeyValueStore& args,
                                     Error* error);
 
@@ -787,7 +787,7 @@ class Manager : public base::SupportsWeakPtr<Manager> {
     power_manager_.reset(power_manager);
   }
 
-  DeviceRefPtr GetDeviceConnectedToService(ServiceRefPtr service);
+  DeviceRefPtr GetDeviceConnectedToService(const ServiceRefPtr& service);
 
   void DeregisterDeviceByLinkName(const std::string& link_name);
 
diff --git a/manager_unittest.cc b/manager_unittest.cc
index fbed9678..2de1d52e 100644
--- a/manager_unittest.cc
+++ b/manager_unittest.cc
@@ -202,9 +202,9 @@ class ManagerTest : public PropertyStoreTest {
     auto devices = manager()->FilterByTechnology(tech);
     return (devices.size() == 1 && devices[0].get() == device.get());
   }
-  bool ServiceOrderIs(ServiceRefPtr svc1, ServiceRefPtr svc2);
+  bool ServiceOrderIs(const ServiceRefPtr& svc1, const ServiceRefPtr& svc2);
 
-  void AdoptProfile(Manager* manager, ProfileRefPtr profile) {
+  void AdoptProfile(Manager* manager, const ProfileRefPtr& profile) {
     manager->profiles_.push_back(profile);
   }
 
@@ -518,7 +518,7 @@ class ManagerTest : public PropertyStoreTest {
 
 const char ManagerTest::TerminationActionTest::kActionName[] = "action";
 
-bool ManagerTest::ServiceOrderIs(ServiceRefPtr svc0, ServiceRefPtr svc1) {
+bool ManagerTest::ServiceOrderIs(const ServiceRefPtr& svc0, const ServiceRefPtr& svc1) {
   if (!manager()->sort_services_task_.IsCancelled()) {
     manager()->SortServicesTask();
   }
diff --git a/mock_connection_health_checker.h b/mock_connection_health_checker.h
index 062c6bb1..fc2a3997 100644
--- a/mock_connection_health_checker.h
+++ b/mock_connection_health_checker.h
@@ -35,7 +35,7 @@ class MockConnectionHealthChecker : public ConnectionHealthChecker {
   ~MockConnectionHealthChecker() override;
 
   MOCK_METHOD1(AddRemoteURL, void(const std::string& url_string));
-  MOCK_METHOD1(AddRemoteIP, void(IPAddress ip));
+  MOCK_METHOD1(AddRemoteIP, void(const IPAddress& ip));
   MOCK_METHOD0(Start, void());
   MOCK_METHOD0(Stop, void());
   MOCK_CONST_METHOD0(health_check_in_progress, bool());
diff --git a/net/attribute_list.cc b/net/attribute_list.cc
index 6065c49f..e0844a7f 100644
--- a/net/attribute_list.cc
+++ b/net/attribute_list.cc
@@ -38,7 +38,7 @@ using std::string;
 namespace shill {
 
 bool AttributeList::CreateAttribute(
-    int id, AttributeList::NewFromIdMethod factory) {
+    int id, const AttributeList::NewFromIdMethod& factory) {
   if (ContainsKey(attributes_, id)) {
     VLOG(7) << "Trying to re-add attribute " << id << ", not overwriting";
     return true;
@@ -300,7 +300,7 @@ bool AttributeList::CreateSsidAttribute(int id, const char* id_string) {
   return true;
 }
 
-bool AttributeList::SetStringAttributeValue(int id, string value) {
+bool AttributeList::SetStringAttributeValue(int id, const string& value) {
   NetlinkAttribute* attribute = GetAttribute(id);
   if (!attribute)
     return false;
@@ -361,7 +361,7 @@ bool AttributeList::GetRawAttributeValue(int id,
   return true;
 }
 
-bool AttributeList::SetRawAttributeValue(int id, ByteString value) {
+bool AttributeList::SetRawAttributeValue(int id, const ByteString& value) {
   NetlinkAttribute* attribute = GetAttribute(id);
   if (!attribute)
     return false;
diff --git a/net/attribute_list.h b/net/attribute_list.h
index 18f325bf..6d1a45d0 100644
--- a/net/attribute_list.h
+++ b/net/attribute_list.h
@@ -49,7 +49,7 @@ class SHILL_EXPORT AttributeList : public base::RefCounted<AttributeList> {
 
   // Instantiates an NetlinkAttribute of the appropriate type from |id|,
   // and adds it to |attributes_|.
-  bool CreateAttribute(int id, NewFromIdMethod factory);
+  bool CreateAttribute(int id, const NewFromIdMethod& factory);
 
   // Helper function for creating control attribute.
   bool CreateControlAttribute(int id);
@@ -117,7 +117,7 @@ class SHILL_EXPORT AttributeList : public base::RefCounted<AttributeList> {
   bool CreateStringAttribute(int id, const char* id_string);
   // SSID attributes are derived from string attributes.
   bool CreateSsidAttribute(int id, const char* id_string);
-  bool SetStringAttributeValue(int id, std::string value);
+  bool SetStringAttributeValue(int id, const std::string& value);
   bool GetStringAttributeValue(int id, std::string* value) const;
 
   bool CreateNestedAttribute(int id, const char* id_string);
@@ -129,7 +129,7 @@ class SHILL_EXPORT AttributeList : public base::RefCounted<AttributeList> {
   bool CreateRawAttribute(int id, const char* id_string);
   // |value| should point to the data (after the |nlattr| header, if there is
   // one).
-  bool SetRawAttributeValue(int id, ByteString value);
+  bool SetRawAttributeValue(int id, const ByteString& value);
   bool GetRawAttributeValue(int id, ByteString* output) const;
 
   // This retrieves a string from any kind of attribute.
diff --git a/net/event_history.cc b/net/event_history.cc
index cd269f74..c0992853 100644
--- a/net/event_history.cc
+++ b/net/event_history.cc
@@ -50,7 +50,7 @@ std::vector<std::string> EventHistory::ExtractWallClockToStrings() const {
   return strings;
 }
 
-void EventHistory::RecordEventInternal(Timestamp now) {
+void EventHistory::RecordEventInternal(const Timestamp& now) {
   events_.push_back(now);
   while (!events_.empty() && max_events_specified_ &&
          (events_.size() > static_cast<size_t>(max_events_saved_))) {
diff --git a/net/event_history.h b/net/event_history.h
index 615262d9..9b2ac878 100644
--- a/net/event_history.h
+++ b/net/event_history.h
@@ -82,7 +82,7 @@ class SHILL_EXPORT EventHistory {
   friend class ServiceTest;  // RecordEventInternal, time_
   friend class WakeOnWiFiTest;  // time_
 
-  void RecordEventInternal(Timestamp now);
+  void RecordEventInternal(const Timestamp& now);
 
   void ExpireEventsBeforeInternal(int seconds_ago, Timestamp now,
                                   ClockType clock_type);
diff --git a/net/event_history_unittest.cc b/net/event_history_unittest.cc
index fe4eb15d..80c8f54a 100644
--- a/net/event_history_unittest.cc
+++ b/net/event_history_unittest.cc
@@ -61,18 +61,18 @@ class EventHistoryTest : public ::testing::Test {
 
   deque<Timestamp>* GetEvents() { return &event_history_->events_; }
 
-  void RecordEvent(Timestamp now) {
+  void RecordEvent(const Timestamp& now) {
     EXPECT_CALL(time_, GetNow()).WillOnce(Return(now));
     event_history_->RecordEvent();
   }
 
-  void ExpireEventsBefore(int seconds_ago, Timestamp now,
+  void ExpireEventsBefore(int seconds_ago, const Timestamp& now,
                           EventHistory::ClockType clock_type) {
     EXPECT_CALL(time_, GetNow()).WillOnce(Return(now));
     event_history_->ExpireEventsBefore(seconds_ago, clock_type);
   }
 
-  void RecordEventAndExpireEventsBefore(int seconds_ago, Timestamp now,
+  void RecordEventAndExpireEventsBefore(int seconds_ago, const Timestamp& now,
                                         EventHistory::ClockType clock_type) {
     EXPECT_CALL(time_, GetNow()).WillOnce(Return(now));
     event_history_->RecordEventAndExpireEventsBefore(seconds_ago, clock_type);
@@ -91,7 +91,7 @@ class EventHistoryTest : public ::testing::Test {
 
   int CountEventsWithinInterval(int seconds_ago,
                                 EventHistory::ClockType clock_type,
-                                Timestamp now) {
+                                const Timestamp& now) {
     EXPECT_CALL(time_, GetNow()).WillOnce(Return(now));
     return event_history_->CountEventsWithinInterval(seconds_ago, clock_type);
   }
diff --git a/net/netlink_attribute.cc b/net/netlink_attribute.cc
index 3248a499..2d3d1955 100644
--- a/net/netlink_attribute.cc
+++ b/net/netlink_attribute.cc
@@ -356,7 +356,7 @@ bool NetlinkAttribute::GetStringValue(string* value) const {
   return false;
 }
 
-bool NetlinkAttribute::SetStringValue(string value) {
+bool NetlinkAttribute::SetStringValue(const string& value) {
   LOG(ERROR) << "Attribute is not of type 'String'";
   return false;
 }
@@ -382,7 +382,7 @@ bool NetlinkAttribute::GetRawValue(ByteString* value) const {
   return false;
 }
 
-bool NetlinkAttribute::SetRawValue(const ByteString new_value) {
+bool NetlinkAttribute::SetRawValue(const ByteString& new_value) {
   LOG(ERROR) << "Attribute is not of type 'Raw'";
   return false;
 }
@@ -745,7 +745,7 @@ bool NetlinkStringAttribute::GetStringValue(string* output) const {
   return true;
 }
 
-bool NetlinkStringAttribute::SetStringValue(const string new_value) {
+bool NetlinkStringAttribute::SetStringValue(const string& new_value) {
   value_ = new_value;
   has_a_value_ = true;
   return true;
@@ -1049,7 +1049,7 @@ bool NetlinkRawAttribute::GetRawValue(ByteString* output) const {
   return true;
 }
 
-bool NetlinkRawAttribute::SetRawValue(const ByteString new_value) {
+bool NetlinkRawAttribute::SetRawValue(const ByteString& new_value) {
   data_ = new_value;
   has_a_value_ = true;
   return true;
diff --git a/net/netlink_attribute.h b/net/netlink_attribute.h
index b1ab1500..2736c642 100644
--- a/net/netlink_attribute.h
+++ b/net/netlink_attribute.h
@@ -90,7 +90,7 @@ class SHILL_EXPORT NetlinkAttribute {
   virtual bool SetFlagValue(bool value);
 
   virtual bool GetStringValue(std::string* value) const;
-  virtual bool SetStringValue(const std::string value);
+  virtual bool SetStringValue(const std::string& value);
 
   virtual bool GetNestedAttributeList(AttributeListRefPtr* value);
   virtual bool ConstGetNestedAttributeList(
@@ -98,7 +98,7 @@ class SHILL_EXPORT NetlinkAttribute {
   virtual bool SetNestedHasAValue();
 
   virtual bool GetRawValue(ByteString* value) const;
-  virtual bool SetRawValue(const ByteString value);
+  virtual bool SetRawValue(const ByteString& value);
 
   // Prints the attribute info -- for debugging.
   virtual void Print(int log_level, int indent) const;
@@ -243,7 +243,7 @@ class SHILL_EXPORT NetlinkStringAttribute : public NetlinkAttribute {
       : NetlinkAttribute(id, id_string, kType, kMyTypeString) {}
   virtual bool InitFromValue(const ByteString& data);
   virtual bool GetStringValue(std::string* value) const;
-  virtual bool SetStringValue(const std::string new_value);
+  virtual bool SetStringValue(const std::string& new_value);
   virtual bool ToString(std::string* value) const;
   virtual ByteString Encode() const;
   std::string value() const { return value_; }
@@ -292,7 +292,7 @@ class NetlinkNestedAttribute : public NetlinkAttribute {
   struct NestedData {
     typedef base::Callback<bool (AttributeList* list, size_t id,
                                  const std::string& attribute_name,
-                                 ByteString data)> AttributeParser;
+                                 const ByteString& data)> AttributeParser;
     typedef std::map<size_t, NestedData> NestedDataMap;
 
     NestedData();
@@ -369,7 +369,7 @@ class NetlinkRawAttribute : public NetlinkAttribute {
   // Gets the value of the data (the header is not stored).
   virtual bool GetRawValue(ByteString* value) const;
   // Should set the value of the data (not the attribute header).
-  virtual bool SetRawValue(const ByteString value);
+  virtual bool SetRawValue(const ByteString& value);
   virtual bool ToString(std::string* value) const;
   virtual ByteString Encode() const;
 
diff --git a/net/netlink_message.cc b/net/netlink_message.cc
index 752f0984..a4469a38 100644
--- a/net/netlink_message.cc
+++ b/net/netlink_message.cc
@@ -267,7 +267,7 @@ void UnknownMessage::Print(int header_log_level,
 //
 
 bool NetlinkMessageFactory::AddFactoryMethod(uint16_t message_type,
-                                             FactoryMethod factory) {
+                                             const FactoryMethod& factory) {
   if (ContainsKey(factories_, message_type)) {
     LOG(WARNING) << "Message type " << message_type << " already exists.";
     return false;
diff --git a/net/netlink_message.h b/net/netlink_message.h
index 5a879549..37e84c73 100644
--- a/net/netlink_message.h
+++ b/net/netlink_message.h
@@ -243,7 +243,7 @@ class SHILL_EXPORT NetlinkMessageFactory {
 
   // Adds a message factory for a specific message_type.  Intended to be used
   // at initialization.
-  bool AddFactoryMethod(uint16_t message_type, FactoryMethod factory);
+  bool AddFactoryMethod(uint16_t message_type, const FactoryMethod& factory);
 
   // Ownership of the message is passed to the caller and, as such, he should
   // delete it.
diff --git a/net/nl80211_attribute.cc b/net/nl80211_attribute.cc
index 89600c15..54b5877f 100644
--- a/net/nl80211_attribute.cc
+++ b/net/nl80211_attribute.cc
@@ -123,7 +123,7 @@ Nl80211AttributeBss::Nl80211AttributeBss()
 
 bool Nl80211AttributeBss::ParseInformationElements(
     AttributeList* attribute_list, size_t id, const string& attribute_name,
-    ByteString data) {
+    const ByteString& data) {
   if (!attribute_list) {
     LOG(ERROR) << "NULL |attribute_list| parameter";
     return false;
diff --git a/net/nl80211_attribute.h b/net/nl80211_attribute.h
index b9a793a9..71c0e7a3 100644
--- a/net/nl80211_attribute.h
+++ b/net/nl80211_attribute.h
@@ -581,7 +581,7 @@ class Nl80211AttributeBss : public NetlinkNestedAttribute {
   static bool ParseInformationElements(AttributeList* attribute_list,
                                        size_t id,
                                        const std::string& attribute_name,
-                                       ByteString data);
+                                       const ByteString& data);
 
   DISALLOW_COPY_AND_ASSIGN(Nl80211AttributeBss);
 };
diff --git a/net/rtnl_message_unittest.cc b/net/rtnl_message_unittest.cc
index 3e74d93c..9824526f 100644
--- a/net/rtnl_message_unittest.cc
+++ b/net/rtnl_message_unittest.cc
@@ -389,10 +389,10 @@ class RTNLMessageTest : public Test {
                      int interface_index,
                      unsigned int flags,
                      unsigned int change,
-                     ByteString address,
-                     ByteString name,
+                     const ByteString& address,
+                     const ByteString& name,
                      uint32_t mtu,
-                     ByteString qdisc,
+                     const ByteString& qdisc,
                      int oper_state) {
     RTNLMessage msg;
     EXPECT_TRUE(msg.Decode(packet));
diff --git a/scope_logger.cc b/scope_logger.cc
index 815503f4..a5b515bf 100644
--- a/scope_logger.cc
+++ b/scope_logger.cc
@@ -154,7 +154,7 @@ void ScopeLogger::EnableScopesByName(const string& expression) {
 }
 
 void ScopeLogger::RegisterScopeEnableChangedCallback(
-    Scope scope, ScopeEnableChangedCallback callback) {
+    Scope scope, const ScopeEnableChangedCallback& callback) {
   CHECK_GE(scope, 0);
   CHECK_LT(scope, kNumScopes);
   log_scope_callbacks_[scope].push_back(callback);
diff --git a/scope_logger.h b/scope_logger.h
index 3d5a817b..44320975 100644
--- a/scope_logger.h
+++ b/scope_logger.h
@@ -116,7 +116,7 @@ class ScopeLogger {
 
   // Register for log scope enable/disable state changes for |scope|.
   void RegisterScopeEnableChangedCallback(
-      Scope scope, ScopeEnableChangedCallback callback);
+      Scope scope, const ScopeEnableChangedCallback& callback);
 
   // Sets the verbose level for all scopes to |verbose_level|.
   void set_verbose_level(int verbose_level) { verbose_level_ = verbose_level; }
diff --git a/service.cc b/service.cc
index 256ec55b..94bb99e0 100644
--- a/service.cc
+++ b/service.cc
@@ -656,7 +656,7 @@ bool Service::Save(StoreInterface* storage) {
 }
 
 void Service::Configure(const KeyValueStore& args, Error* error) {
-  for (const auto it : args.properties()) {
+  for (const auto& it : args.properties()) {
     if (it.second.IsTypeCompatible<bool>()) {
       if (ContainsKey(parameters_ignored_for_configure_, it.first)) {
         SLOG(this, 5) << "Ignoring bool property: " << it.first;
@@ -1061,8 +1061,8 @@ uint16_t Service::SecurityLevel() {
 
 // static
 bool Service::Compare(Manager* manager,
-                      ServiceRefPtr a,
-                      ServiceRefPtr b,
+                      const ServiceRefPtr& a,
+                      const ServiceRefPtr& b,
                       bool compare_connectivity_state,
                       const vector<Technology::Identifier>& tech_order,
                       const char** reason) {
diff --git a/service.h b/service.h
index e35d17d2..2cfe7ad5 100644
--- a/service.h
+++ b/service.h
@@ -448,8 +448,8 @@ class Service : public base::RefCounted<Service> {
   // difference.  |reason| is populated with the exact criteria used for the
   // ultimate comparison.
   static bool Compare(Manager* manager,
-                      ServiceRefPtr a,
-                      ServiceRefPtr b,
+                      const ServiceRefPtr& a,
+                      const ServiceRefPtr& b,
                       bool compare_connectivity_state,
                       const std::vector<Technology::Identifier>& tech_order,
                       const char** reason);
@@ -686,9 +686,9 @@ class Service : public base::RefCounted<Service> {
   friend class WiFiServiceTest;
   friend class WiMaxProviderTest;
   friend class WiMaxServiceTest;
-  friend void TestCommonPropertyChanges(ServiceRefPtr, ServiceMockAdaptor*);
-  friend void TestCustomSetterNoopChange(ServiceRefPtr, MockManager*);
-  friend void TestNamePropertyChange(ServiceRefPtr, ServiceMockAdaptor*);
+  friend void TestCommonPropertyChanges(const ServiceRefPtr&, ServiceMockAdaptor*);
+  friend void TestCustomSetterNoopChange(const ServiceRefPtr&, MockManager*);
+  friend void TestNamePropertyChange(const ServiceRefPtr&, ServiceMockAdaptor*);
   FRIEND_TEST(AllMockServiceTest, AutoConnectWithFailures);
   FRIEND_TEST(CellularCapabilityGSMTest, SetStorageIdentifier);
   FRIEND_TEST(CellularServiceTest, IsAutoConnectable);
diff --git a/service_property_change_notifier.cc b/service_property_change_notifier.cc
index 97888c1c..2e9d704f 100644
--- a/service_property_change_notifier.cc
+++ b/service_property_change_notifier.cc
@@ -34,7 +34,7 @@ ServicePropertyChangeNotifier::ServicePropertyChangeNotifier(
 ServicePropertyChangeNotifier::~ServicePropertyChangeNotifier() {}
 
 void ServicePropertyChangeNotifier::AddBoolPropertyObserver(
-    const string& name, BoolAccessor accessor) {
+    const string& name, const BoolAccessor& accessor) {
   property_observers_.emplace_back(
       new PropertyObserver<bool>(
           accessor,
@@ -44,7 +44,7 @@ void ServicePropertyChangeNotifier::AddBoolPropertyObserver(
 }
 
 void ServicePropertyChangeNotifier::AddUint8PropertyObserver(
-    const string& name, Uint8Accessor accessor) {
+    const string& name, const Uint8Accessor& accessor) {
   property_observers_.emplace_back(
       new PropertyObserver<uint8_t>(
           accessor,
@@ -54,7 +54,7 @@ void ServicePropertyChangeNotifier::AddUint8PropertyObserver(
 }
 
 void ServicePropertyChangeNotifier::AddUint16PropertyObserver(
-    const string& name, Uint16Accessor accessor) {
+    const string& name, const Uint16Accessor& accessor) {
   property_observers_.emplace_back(
       new PropertyObserver<uint16_t>(
           accessor,
@@ -64,7 +64,7 @@ void ServicePropertyChangeNotifier::AddUint16PropertyObserver(
 }
 
 void ServicePropertyChangeNotifier::AddUint16sPropertyObserver(
-    const string& name, Uint16sAccessor accessor) {
+    const string& name, const Uint16sAccessor& accessor) {
   property_observers_.emplace_back(
       new PropertyObserver<Uint16s>(
           accessor,
@@ -74,7 +74,7 @@ void ServicePropertyChangeNotifier::AddUint16sPropertyObserver(
 }
 
 void ServicePropertyChangeNotifier::AddUintPropertyObserver(
-    const string& name, Uint32Accessor accessor) {
+    const string& name, const Uint32Accessor& accessor) {
   property_observers_.emplace_back(
       new PropertyObserver<uint32_t>(
           accessor,
@@ -84,7 +84,7 @@ void ServicePropertyChangeNotifier::AddUintPropertyObserver(
 }
 
 void ServicePropertyChangeNotifier::AddIntPropertyObserver(
-    const string& name, Int32Accessor accessor) {
+    const string& name, const Int32Accessor& accessor) {
   property_observers_.emplace_back(
       new PropertyObserver<int32_t>(
           accessor,
@@ -94,7 +94,7 @@ void ServicePropertyChangeNotifier::AddIntPropertyObserver(
 }
 
 void ServicePropertyChangeNotifier::AddRpcIdentifierPropertyObserver(
-    const string& name, RpcIdentifierAccessor accessor) {
+    const string& name, const RpcIdentifierAccessor& accessor) {
   property_observers_.emplace_back(
       new PropertyObserver<string>(
           accessor,
@@ -104,7 +104,7 @@ void ServicePropertyChangeNotifier::AddRpcIdentifierPropertyObserver(
 }
 
 void ServicePropertyChangeNotifier::AddStringPropertyObserver(
-    const string& name, StringAccessor accessor) {
+    const string& name, const StringAccessor& accessor) {
   property_observers_.emplace_back(
       new PropertyObserver<string>(
           accessor,
@@ -114,7 +114,7 @@ void ServicePropertyChangeNotifier::AddStringPropertyObserver(
 }
 
 void ServicePropertyChangeNotifier::AddStringmapPropertyObserver(
-    const string& name, StringmapAccessor accessor) {
+    const string& name, const StringmapAccessor& accessor) {
   property_observers_.emplace_back(
       new PropertyObserver<Stringmap>(
           accessor,
diff --git a/service_property_change_notifier.h b/service_property_change_notifier.h
index d60ee5e2..ff7814d9 100644
--- a/service_property_change_notifier.h
+++ b/service_property_change_notifier.h
@@ -42,23 +42,23 @@ class ServicePropertyChangeNotifier {
   virtual ~ServicePropertyChangeNotifier();
 
   virtual void AddBoolPropertyObserver(const std::string& name,
-                                       BoolAccessor accessor);
+                                       const BoolAccessor& accessor);
   virtual void AddUint8PropertyObserver(const std::string& name,
-                                        Uint8Accessor accessor);
+                                        const Uint8Accessor& accessor);
   virtual void AddUint16PropertyObserver(const std::string& name,
-                                         Uint16Accessor accessor);
+                                         const Uint16Accessor& accessor);
   virtual void AddUint16sPropertyObserver(const std::string& name,
-                                          Uint16sAccessor accessor);
+                                          const Uint16sAccessor& accessor);
   virtual void AddUintPropertyObserver(const std::string& name,
-                                       Uint32Accessor accessor);
+                                       const Uint32Accessor& accessor);
   virtual void AddIntPropertyObserver(const std::string& name,
-                                      Int32Accessor accessor);
+                                      const Int32Accessor& accessor);
   virtual void AddRpcIdentifierPropertyObserver(const std::string& name,
-                                                RpcIdentifierAccessor accessor);
+                                                const RpcIdentifierAccessor& accessor);
   virtual void AddStringPropertyObserver(const std::string& name,
-                                         StringAccessor accessor);
+                                         const StringAccessor& accessor);
   virtual void AddStringmapPropertyObserver(const std::string& name,
-                                            StringmapAccessor accessor);
+                                            const StringmapAccessor& accessor);
   virtual void UpdatePropertyObservers();
 
  private:
diff --git a/service_property_change_test.cc b/service_property_change_test.cc
index 4f214ffd..22abae40 100644
--- a/service_property_change_test.cc
+++ b/service_property_change_test.cc
@@ -45,7 +45,7 @@ namespace shill {
 // for specific setters. However, it's convenient to have all the property
 // change notifications documented (and tested) in one place.
 
-void TestCommonPropertyChanges(ServiceRefPtr service,
+void TestCommonPropertyChanges(const ServiceRefPtr& service,
                                ServiceMockAdaptor* adaptor) {
   Error error;
 
@@ -119,7 +119,7 @@ void TestCommonPropertyChanges(ServiceRefPtr service,
   Mock::VerifyAndClearExpectations(adaptor);
 }
 
-void TestAutoConnectPropertyChange(ServiceRefPtr service,
+void TestAutoConnectPropertyChange(const ServiceRefPtr& service,
                                    ServiceMockAdaptor* adaptor) {
   bool auto_connect = service->auto_connect();
   EXPECT_CALL(*adaptor, EmitBoolChanged(kAutoConnectProperty, _));
@@ -127,7 +127,7 @@ void TestAutoConnectPropertyChange(ServiceRefPtr service,
   Mock::VerifyAndClearExpectations(adaptor);
 }
 
-void TestNamePropertyChange(ServiceRefPtr service,
+void TestNamePropertyChange(const ServiceRefPtr& service,
                             ServiceMockAdaptor* adaptor) {
   Error error;
   string name = service->GetNameProperty(&error);
@@ -136,7 +136,7 @@ void TestNamePropertyChange(ServiceRefPtr service,
   Mock::VerifyAndClearExpectations(adaptor);
 }
 
-void TestCustomSetterNoopChange(ServiceRefPtr service,
+void TestCustomSetterNoopChange(const ServiceRefPtr& service,
                                 MockManager* mock_manager) {
   // SetAutoConnectFull
   {
diff --git a/service_property_change_test.h b/service_property_change_test.h
index a49aa5c3..adb56581 100644
--- a/service_property_change_test.h
+++ b/service_property_change_test.h
@@ -26,15 +26,15 @@ class ServiceMockAdaptor;
 
 // Test property change notifications that are implemented by all
 // Services.
-void TestCommonPropertyChanges(ServiceRefPtr service,
+void TestCommonPropertyChanges(const ServiceRefPtr& service,
                                ServiceMockAdaptor* adaptor);
 // Test AutoConnect property change notification. Implemented by
 // all Services except EthernetService.
-void TestAutoConnectPropertyChange(ServiceRefPtr service,
+void TestAutoConnectPropertyChange(const ServiceRefPtr& service,
                                    ServiceMockAdaptor* adaptor);
 // Test Name property change notification. Only VPNService allows
 // changing the name property.
-void TestNamePropertyChange(ServiceRefPtr service,
+void TestNamePropertyChange(const ServiceRefPtr& service,
                            ServiceMockAdaptor* adaptor);
 // Test that the common customer setters (for all Services) return
 // false if setting to the same as the current value.
diff --git a/service_sorter.h b/service_sorter.h
index eb56b998..d9a92379 100644
--- a/service_sorter.h
+++ b/service_sorter.h
@@ -38,7 +38,7 @@ class ServiceSorter {
       : manager_(manager),
         compare_connectivity_state_(compare_connectivity_state),
         technology_order_(tech_order) {}
-  bool operator() (ServiceRefPtr a, ServiceRefPtr b) {
+  bool operator() (const ServiceRefPtr& a, const ServiceRefPtr& b) {
     const char* reason;
     return Service::Compare(manager_, a, b, compare_connectivity_state_,
                             technology_order_, &reason);
diff --git a/socket_info_unittest.cc b/socket_info_unittest.cc
index e9f53f75..65947622 100644
--- a/socket_info_unittest.cc
+++ b/socket_info_unittest.cc
@@ -57,7 +57,7 @@ TEST_F(SocketInfoTest, CopyConstructor) {
                   20,
                   SocketInfo::kTimerStateRetransmitTimerPending);
 
-  SocketInfo info_copy(info);
+  const SocketInfo& info_copy(info);
   ExpectSocketInfoEqual(info, info_copy);
 }
 
@@ -73,7 +73,7 @@ TEST_F(SocketInfoTest, AssignmentOperator) {
                   20,
                   SocketInfo::kTimerStateRetransmitTimerPending);
 
-  SocketInfo info_copy = info;
+  const SocketInfo& info_copy = info;
   ExpectSocketInfoEqual(info, info_copy);
 }
 
diff --git a/test-rpc-proxy/proxy_rpc_in_data_types.cc b/test-rpc-proxy/proxy_rpc_in_data_types.cc
index 1e24f5d2..b9746d02 100644
--- a/test-rpc-proxy/proxy_rpc_in_data_types.cc
+++ b/test-rpc-proxy/proxy_rpc_in_data_types.cc
@@ -23,7 +23,7 @@ static const char kXmlRpcStructTypeKey[] = "xmlrpc_struct_type_key";
 
 void AssertStructTypeStringFromXmlRpcValue(
     XmlRpc::XmlRpcValue* xml_rpc_value_in,
-    std::string expected_type) {
+    const std::string& expected_type) {
   if ((*xml_rpc_value_in)[kXmlRpcStructTypeKey] != expected_type) {
     LOG(FATAL) << "Unexpected object received. Expected: " << expected_type
                << "Recieved: " << (*xml_rpc_value_in)[kXmlRpcStructTypeKey];
diff --git a/vpn/vpn_provider.cc b/vpn/vpn_provider.cc
index b9965b61..163037c8 100644
--- a/vpn/vpn_provider.cc
+++ b/vpn/vpn_provider.cc
@@ -181,7 +181,7 @@ bool VPNProvider::OnDeviceInfoAvailable(const string& link_name,
   return false;
 }
 
-void VPNProvider::RemoveService(VPNServiceRefPtr service) {
+void VPNProvider::RemoveService(const VPNServiceRefPtr& service) {
   const auto it = std::find(services_.begin(), services_.end(), service);
   if (it != services_.end()) {
     services_.erase(it);
diff --git a/vpn/vpn_provider.h b/vpn/vpn_provider.h
index 08c8923f..3bd2d907 100644
--- a/vpn/vpn_provider.h
+++ b/vpn/vpn_provider.h
@@ -68,7 +68,7 @@ class VPNProvider : public ProviderInterface {
   // Clean up a VPN services that has been unloaded and will be deregistered.
   // This removes the VPN provider's reference to this service in its
   // services_ vector.
-  void RemoveService(VPNServiceRefPtr service);
+  void RemoveService(const VPNServiceRefPtr& service);
 
   // Returns true if any of the managed VPN services is connecting or connected.
   virtual bool HasActiveService() const;