Lock out GCs while iterating over MediaStreamSource audio consumers.

third_party/WebKit/Source/platform/mediastream/MediaStreamSource.cpp

Index: third_party/WebKit/Source/platform/mediastream/MediaStreamSource.cpp
diff --git a/third_party/WebKit/Source/platform/mediastream/MediaStreamSource.cpp b/third_party/WebKit/Source/platform/mediastream/MediaStreamSource.cpp
index da4b301ee37423105f552f9fc934d130b04c7792..ca12e1c9fb79b62562e07491d45e500f71a78aa7 100644
--- a/third_party/WebKit/Source/platform/mediastream/MediaStreamSource.cpp
+++ b/third_party/WebKit/Source/platform/mediastream/MediaStreamSource.cpp
@@ -107,6 +107,9 @@ void MediaStreamSource::setAudioFormat(size_t numberOfChannels,
 void MediaStreamSource::consumeAudio(AudioBus* bus, size_t numberOfFrames) {
   ASSERT(m_requiresConsumer);
   MutexLocker locker(m_audioConsumersLock);
+  // Prevent GCs from going ahead while this iteration runs, attempting to
+  // pinpoint crbug.com/682945 failures.
+  ThreadState::MainThreadGCForbiddenScope scope;
   for (AudioDestinationConsumer* consumer : m_audioConsumers)
     consumer->consumeAudio(bus, numberOfFrames);
 }