Handle Alpha channel in Canvas capture

content/renderer/pepper/pepper_media_stream_video_track_host.cc

 // 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.
 
 #include "content/renderer/pepper/pepper_media_stream_video_track_host.h"
 
 #include <stddef.h>
 
 #include "base/base64.h"
 #include "base/logging.h"
@@ skipping 357 matching lines @@
   SendEnqueueBufferMessageToPlugin(index);
   return PP_OK;
 }
 
 void PepperMediaStreamVideoTrackHost::OnVideoFrame(
     const scoped_refptr<VideoFrame>& frame,
     base::TimeTicks estimated_capture_time) {
   DCHECK(frame.get());
   // TODO(penghuang): Check |frame->end_of_stream()| and close the track.
   PP_VideoFrame_Format ppformat = ToPpapiFormat(frame->format());
+
+  // Drop alpha channel since we do not support it yet.
+  if (frame->format() == media::PIXEL_FORMAT_YV12A)
+    frame->DropYV12AAlphaChannel();
+
   if (ppformat == PP_VIDEOFRAME_FORMAT_UNKNOWN)
     return;
 
   if (source_frame_size_.IsEmpty()) {
     source_frame_size_ = frame->visible_rect().size();
     source_frame_format_ = ppformat;
     InitBuffers();
   }
 
   int32_t index = buffer_manager()->DequeueBuffer();
@@ skipping 139 matching lines @@
 }
 
 void PepperMediaStreamVideoTrackHost::OnTrackStarted(
     MediaStreamSource* source,
     MediaStreamRequestResult result,
     const blink::WebString& result_name) {
   DVLOG(3) << "OnTrackStarted result: " << result;
 }
 
 }  // namespace content