Change DtmfSenderHandler to handle events on the signaling thread.

content/renderer/media/webrtc/media_stream_remote_video_source.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_RENDERER_MEDIA_WEBRTC_MEDIA_STREAM_REMOTE_VIDEO_SOURCE_H_
 #define CONTENT_RENDERER_MEDIA_WEBRTC_MEDIA_STREAM_REMOTE_VIDEO_SOURCE_H_
 
 #include "base/memory/weak_ptr.h"
 #include "base/single_thread_task_runner.h"
 #include "content/common/content_export.h"
@@ skipping 27 matching lines @@
     friend class MediaStreamRemoteVideoSource;
     void SetSource(const base::WeakPtr<MediaStreamRemoteVideoSource>& source);
 
     // webrtc::ObserverInterface implementation.
     void OnChanged() override;
 
     void OnChangedImpl(webrtc::MediaStreamTrackInterface::TrackState state);
 
     const scoped_refptr<base::SingleThreadTaskRunner> main_thread_;
     base::WeakPtr<MediaStreamRemoteVideoSource> source_;
+#if DCHECK_IS_ON
+    bool source_set_;
+#endif
     const scoped_refptr<webrtc::VideoTrackInterface> track_;
     webrtc::MediaStreamTrackInterface::TrackState state_;
   };
 
   MediaStreamRemoteVideoSource(const scoped_refptr<Observer>& observer);
   virtual ~MediaStreamRemoteVideoSource();
 
  protected:
   // Implements MediaStreamVideoSource.
   void GetCurrentSupportedFormats(
@@ skipping 23 matching lines @@
   class RemoteVideoSourceDelegate;
   scoped_refptr<RemoteVideoSourceDelegate> delegate_;
   base::WeakPtrFactory<MediaStreamRemoteVideoSource> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaStreamRemoteVideoSource);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_WEBRTC_MEDIA_STREAM_REMOTE_VIDEO_SOURCE_H_