Support alpha channel recording for VPX in MediaRecorder

content/renderer/media_recorder/video_track_recorder.h

 // Copyright 2015 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_RECORDER_VIDEO_TRACK_RECORDER_H_
 #define CONTENT_RENDERER_MEDIA_RECORDER_VIDEO_TRACK_RECORDER_H_
 
 #include <memory>
 
 #include "base/macros.h"
@@ skipping 33 matching lines @@
 #if BUILDFLAG(RTC_USE_H264)
     H264,
 #endif
     LAST
   };
   class Encoder;
 
   using OnEncodedVideoCB =
       base::Callback<void(const media::WebmMuxer::VideoParameters& params,
                           std::unique_ptr<std::string> encoded_data,
+                          std::unique_ptr<std::string> encoded_alpha,
                           base::TimeTicks capture_timestamp,
                           bool is_key_frame)>;
 
   static CodecId GetPreferredCodecId();
 
   VideoTrackRecorder(CodecId codec,
                      const blink::WebMediaStreamTrack& track,
                      const OnEncodedVideoCB& on_encoded_video_cb,
                      int32_t bits_per_second);
   ~VideoTrackRecorder() override;
 
   void Pause();
   void Resume();
 
   void OnVideoFrameForTesting(const scoped_refptr<media::VideoFrame>& frame,
                               base::TimeTicks capture_time);
  private:
   friend class VideoTrackRecorderTest;
 
   void InitializeEncoder(CodecId codec,
                          const OnEncodedVideoCB& on_encoded_video_callback,
                          int32_t bits_per_second,
                          const scoped_refptr<media::VideoFrame>& frame,
                          base::TimeTicks capture_time);
 
+  // TODO(emircan): Remove after refactor, see http://crbug.com/700433.
+  bool CanEncodeAlphaChannelForTesting();
+
   // Used to check that we are destroyed on the same thread we were created.
   base::ThreadChecker main_render_thread_checker_;
 
   // We need to hold on to the Blink track to remove ourselves on dtor.
   blink::WebMediaStreamTrack track_;
 
   // Inner class to encode using whichever codec is configured.
   scoped_refptr<Encoder> encoder_;
 
   base::Callback<void(const scoped_refptr<media::VideoFrame>& frame,
                       base::TimeTicks capture_time)>
       initialize_encoder_callback_;
 
   // Used to track the paused state during the initialization process.
   bool paused_before_init_;
 
   base::WeakPtrFactory<VideoTrackRecorder> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoTrackRecorder);
 };
 
 }  // namespace content
 #endif  // CONTENT_RENDERER_MEDIA_RECORDER_VIDEO_TRACK_RECORDER_H_