Remove media::VideoDecodeContext as it has no implementation and is unused.

media/video/ffmpeg_video_decode_engine.h

Index: media/video/ffmpeg_video_decode_engine.h
diff --git a/media/video/ffmpeg_video_decode_engine.h b/media/video/ffmpeg_video_decode_engine.h
index 3bc80c710abdfd125aaadb97e7e10a7f0f8c3137..3ac74118056ffe743d0b371290fe01bd344a0b30 100644
--- a/media/video/ffmpeg_video_decode_engine.h
+++ b/media/video/ffmpeg_video_decode_engine.h
@@ -23,9 +23,7 @@ class MEDIA_EXPORT FFmpegVideoDecodeEngine : public VideoDecodeEngine {
   virtual ~FFmpegVideoDecodeEngine();
 
   // Implementation of the VideoDecodeEngine Interface.
-  virtual void Initialize(MessageLoop* message_loop,
-                          VideoDecodeEngine::EventHandler* event_handler,
-                          VideoDecodeContext* context,
+  virtual void Initialize(VideoDecodeEngine::EventHandler* event_handler,
                           const VideoDecoderConfig& config);
   virtual void ConsumeVideoSample(scoped_refptr<Buffer> buffer);
   virtual void ProduceVideoFrame(scoped_refptr<VideoFrame> frame);