Change a disabled MediaStreamVideoTrack to output black video frames for each incoming frame.

content/renderer/media/mock_media_stream_video_sink.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_MOCK_MEDIA_STREAM_VIDEO_SINK_H_
 #define CONTENT_RENDERER_MEDIA_MOCK_MEDIA_STREAM_VIDEO_SINK_H_
 
 #include "content/public/renderer/media_stream_video_sink.h"
 
 #include "base/memory/weak_ptr.h"
@@ skipping 14 matching lines @@
 
   // Triggered when OnVideoFrame(const scoped_refptr<media::VideoFrame>& frame)
   // is called.
   MOCK_METHOD0(OnVideoFrame, void());
 
   VideoCaptureDeliverFrameCB GetDeliverFrameCB();
 
   int number_of_frames() const { return number_of_frames_; }
   media::VideoFrame::Format format() const { return format_; }
   gfx::Size frame_size() const { return frame_size_; }
+  scoped_refptr<media::VideoFrame> last_frame() const { return last_frame_; };
 
   bool enabled() const { return enabled_; }
   blink::WebMediaStreamSource::ReadyState state() const { return state_; }
 
  private:
   void DeliverVideoFrame(
       const scoped_refptr<media::VideoFrame>& frame,
       const media::VideoCaptureFormat& format,
       const base::TimeTicks& estimated_capture_time);
 
   int number_of_frames_;
   bool enabled_;
   media::VideoFrame::Format format_;
   blink::WebMediaStreamSource::ReadyState state_;
   gfx::Size frame_size_;
+  scoped_refptr<media::VideoFrame> last_frame_;
   base::WeakPtrFactory<MockMediaStreamVideoSink> weak_factory_;
 };
 
 }  // namespace content
 
 #endif