Make FFmpegVideoDecoder defer a flush until the pending read completes.

media/filters/ffmpeg_video_decoder.h

Index: media/filters/ffmpeg_video_decoder.h
diff --git a/media/filters/ffmpeg_video_decoder.h b/media/filters/ffmpeg_video_decoder.h
index cd60c2e2a6ccb59ee2f1476682b8fec96c93995b..912ba581e5ba5160d472f65e2d37a8074fb55367 100644
--- a/media/filters/ffmpeg_video_decoder.h
+++ b/media/filters/ffmpeg_video_decoder.h
@@ -64,6 +64,9 @@ class MEDIA_EXPORT FFmpegVideoDecoder : public VideoDecoder {
   // and resets them to NULL.
   void ReleaseFFmpegResources();
 
+  // Flush decoder and call |flush_cb_|.
+  void DoFlush();
+
   // Allocates a video frame based on the current format and dimensions based on
   // the current state of |codec_context_|.
   scoped_refptr<VideoFrame> AllocateVideoFrame();
@@ -75,6 +78,7 @@ class MEDIA_EXPORT FFmpegVideoDecoder : public VideoDecoder {
   StatisticsCB statistics_cb_;
 
   ReadCB read_cb_;
+  base::Closure flush_cb_;
 
   // FFmpeg structures owned by this object.
   AVCodecContext* codec_context_;