[Stats] Don't attempt to aggregate empty VideoSenderInfos.

This fixes a crash that could happen if substreams exist but there is
no kMedia substream yet. There was an assumption that we either had no
substreams or at least one kMedia substream, but this was not true.
The correct thing to do is to ignore substream stats that are not
associated with any kMedia substream, because we only produce
"outbound-rtp" stats objects for existing kMedia substreams.

A test is added to make sure no stats are returned. Prior to the fix,
this test would crash.

Bug: chromium:1090712
Change-Id: Ib1f8494a162542ae56bdd2df7618775a3473419b
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/176446
Commit-Queue: Henrik Boström <hbos@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#31442}

2 files changed, 24 insertions, 1 deletions

diff --git a/media/engine/webrtc_video_engine.cc b/media/engine/webrtc_video_engine.cc
index 71a0939cb9..3976a6a1c5 100644
--- a/media/engine/webrtc_video_engine.cc
+++ b/media/engine/webrtc_video_engine.cc
@@ -1587,6 +1587,8 @@ void WebRtcVideoChannel::FillSenderStats(VideoMediaInfo* video_media_info,
            send_streams_.begin();
        it != send_streams_.end(); ++it) {
     auto infos = it->second->GetPerLayerVideoSenderInfos(log_stats);
+    if (infos.empty())
+      continue;
     video_media_info->aggregated_senders.push_back(
         it->second->GetAggregatedVideoSenderInfo(infos));
     for (auto&& info : infos) {
@@ -2594,7 +2596,7 @@ VideoSenderInfo
 WebRtcVideoChannel::WebRtcVideoSendStream::GetAggregatedVideoSenderInfo(
     const std::vector<VideoSenderInfo>& infos) const {
   RTC_DCHECK_RUN_ON(&thread_checker_);
-  RTC_DCHECK(!infos.empty());
+  RTC_CHECK(!infos.empty());
   if (infos.size() == 1) {
     return infos[0];
   }
diff --git a/media/engine/webrtc_video_engine_unittest.cc b/media/engine/webrtc_video_engine_unittest.cc
index 1b839e932a..3260ace2d7 100644
--- a/media/engine/webrtc_video_engine_unittest.cc
+++ b/media/engine/webrtc_video_engine_unittest.cc
@@ -5599,6 +5599,27 @@ TEST_F(WebRtcVideoChannelTest, GetPerLayerStatsReportForSubStreams) {
   EXPECT_EQ(sender.rid, absl::nullopt);
 }
 
+TEST_F(WebRtcVideoChannelTest, MediaSubstreamMissingProducesEmpyStats) {
+  FakeVideoSendStream* stream = AddSendStream();
+
+  const uint32_t kRtxSsrc = 123u;
+  const uint32_t kMissingMediaSsrc = 124u;
+
+  // Set up a scenarios where we have a substream that is not kMedia (in this
+  // case: kRtx) but its associated kMedia stream does not exist yet. This
+  // results in zero GetPerLayerVideoSenderInfos despite non-empty substreams.
+  // Covers https://crbug.com/1090712.
+  auto stats = GetInitialisedStats();
+  auto& substream = stats.substreams[kRtxSsrc];
+  substream.type = webrtc::VideoSendStream::StreamStats::StreamType::kRtx;
+  substream.referenced_media_ssrc = kMissingMediaSsrc;
+  stream->SetStats(stats);
+
+  cricket::VideoMediaInfo video_media_info;
+  ASSERT_TRUE(channel_->GetStats(&video_media_info));
+  EXPECT_TRUE(video_media_info.senders.empty());
+}
+
 TEST_F(WebRtcVideoChannelTest, GetStatsReportsUpperResolution) {
   FakeVideoSendStream* stream = AddSendStream();
   webrtc::VideoSendStream::Stats stats;