RemoteMediaStreamImpl using WebRtcMediaStreamTrackMap.

content/renderer/media/webrtc/webrtc_media_stream_track_adapter_map.cc

Index: content/renderer/media/webrtc/webrtc_media_stream_track_adapter_map.cc
diff --git a/content/renderer/media/webrtc/webrtc_media_stream_track_adapter_map.cc b/content/renderer/media/webrtc/webrtc_media_stream_track_adapter_map.cc
index d21937b76f0a74eb0875298ce20c3a4984940078..685e576b1006fc8cbff0ba1c0bd53463dfe7b40d 100644
--- a/content/renderer/media/webrtc/webrtc_media_stream_track_adapter_map.cc
+++ b/content/renderer/media/webrtc/webrtc_media_stream_track_adapter_map.cc
@@ -47,9 +47,8 @@ WebRtcMediaStreamTrackAdapterMap::AdapterRef::~AdapterRef() {
 }
 
 WebRtcMediaStreamTrackAdapterMap::WebRtcMediaStreamTrackAdapterMap(
-    PeerConnectionDependencyFactory* const factory,
-    const scoped_refptr<base::SingleThreadTaskRunner>& main_thread)
-    : factory_(factory), main_thread_(main_thread) {
+    PeerConnectionDependencyFactory* const factory)
+    : factory_(factory), main_thread_(base::ThreadTaskRunnerHandle::Get()) {

[Guido Urdaneta, 2017/06/12 14:25:29]

How do you know this is the main thread?
Shouldn't the variable have another name?

[hbos_chromium, 2017/06/12 15:05:21]

It has to be the main thread since it is used by WebRtcMediaStreamTrackAdapter
which require it to be the main thread. (Which thread its components is
initialized depends on this threading model of main and signaling thread.)

Would you prefer if I pass main_thread in as an argument like before, forcing
the caller to ensure that it is the main thread?

(Code not updated because I have to leave for the day)

[Guido Urdaneta, 2017/06/12 15:18:35]

It's fine this way then. Just add a comment saying that this is intended to be
constructed on the main thread.

   DCHECK(factory_);
   DCHECK(main_thread_);
 }
@@ -90,7 +89,7 @@ std::unique_ptr<WebRtcMediaStreamTrackAdapterMap::AdapterRef>
 WebRtcMediaStreamTrackAdapterMap::GetOrCreateRemoteTrackAdapter(
     webrtc::MediaStreamTrackInterface* webrtc_track) {
   DCHECK(webrtc_track);
-  DCHECK(factory_->GetWebRtcSignalingThread()->BelongsToCurrentThread());
+  DCHECK(!main_thread_->BelongsToCurrentThread());
   return GetOrCreateTrackAdapter(

[Guido Urdaneta, 2017/06/12 14:25:29]

What happens if there are concurrent calls to this from different threads?

[hbos_chromium, 2017/06/12 15:05:21]

This is thread safe thanks to use of lock_.

[hbos_chromium, 2017/06/12 15:07:51]

But the WebRtcMediaStreamTrackAdapter needs this to be on the signaling thread
and doesn't allow other threads to invoke it by design.

[Guido Urdaneta, 2017/06/12 15:18:35]

Acknowledged.

       AdapterRef::Type::kRemote,
       base::Bind(&WebRtcMediaStreamTrackAdapter::CreateRemoteTrackAdapter,