Fix DCHECK crash in RtcVideoEncoder.

content/renderer/media/rtc_video_encoder.h

 // Copyright 2013 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_RTC_VIDEO_ENCODER_H_
 #define CONTENT_RENDERER_MEDIA_RTC_VIDEO_ENCODER_H_
 
 #include <vector>
 
 #include "base/memory/ref_counted.h"
@@ skipping 17 matching lines @@
 class GpuVideoAcceleratorFactories;
 
 }  // namespace media
 
 namespace content {
 
 // RTCVideoEncoder uses a media::VideoEncodeAccelerator to implement a
 // webrtc::VideoEncoder class for WebRTC.  Internally, VEA methods are
 // trampolined to a private RTCVideoEncoder::Impl instance.  The Impl class runs
 // on the worker thread queried from the |gpu_factories_|, which is presently
-// the media thread.  RTCVideoEncoder itself is run and destroyed on the thread
-// it is constructed on, which is presently the libjingle worker thread.
-// Callbacks from the Impl due to its VEA::Client notifications are also posted
-// back to RTCVideoEncoder on this thread.
+// the media thread.  RTCVideoEncoder is sychronized by webrtc::VideoSender.
+// webrtc::VideoEncoder methods do not run concurrently. RTCVideoEncoder is run
+// and destroyed on the thread it is constructed on, which is presently the
+// libjingle worker thread. Encode is run on ViECaptureThread. SetRates and
+// SetChannelParameters are run on ProcessThread or the libjingle worker thread.
+// Callbacks from the Impl due to its VEA::Client notifications are posted back
+// to RTCVideoEncoder on the libjingle worker thread.
 class CONTENT_EXPORT RTCVideoEncoder
     : NON_EXPORTED_BASE(public webrtc::VideoEncoder) {
  public:
   RTCVideoEncoder(
       webrtc::VideoCodecType type,
       media::VideoCodecProfile profile,
       const scoped_refptr<media::GpuVideoAcceleratorFactories>& gpu_factories);
   virtual ~RTCVideoEncoder();
 
   // webrtc::VideoEncoder implementation.  Tasks are posted to |impl_| using the
@@ skipping 51 matching lines @@
   // RTCVideoEncoder.
   // NOTE: Weak pointers must be invalidated before all other member variables.
   base::WeakPtrFactory<RTCVideoEncoder> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(RTCVideoEncoder);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_RTC_VIDEO_ENCODER_H_