Handle Alpha channel in Canvas capture

content/renderer/media/webrtc/webrtc_video_capturer_adapter.cc

Index: content/renderer/media/webrtc/webrtc_video_capturer_adapter.cc
diff --git a/content/renderer/media/webrtc/webrtc_video_capturer_adapter.cc b/content/renderer/media/webrtc/webrtc_video_capturer_adapter.cc
index 962164c2245fa9140aa4c2346f10d7603d96faf5..4b70db38205e2ca8dd72717516956df368289d4d 100644
--- a/content/renderer/media/webrtc/webrtc_video_capturer_adapter.cc
+++ b/content/renderer/media/webrtc/webrtc_video_capturer_adapter.cc
@@ -219,14 +219,20 @@ void WebRtcVideoCapturerAdapter::OnFrameCaptured(
     const scoped_refptr<media::VideoFrame>& frame) {
   DCHECK(thread_checker_.CalledOnValidThread());
   TRACE_EVENT0("video", "WebRtcVideoCapturerAdapter::OnFrameCaptured");
-  if (!(frame->IsMappable() && (frame->format() == media::PIXEL_FORMAT_I420 ||
-                                frame->format() == media::PIXEL_FORMAT_YV12))) {
+  if (!(frame->IsMappable() &&
+        (frame->format() == media::PIXEL_FORMAT_I420 ||
+         frame->format() == media::PIXEL_FORMAT_YV12 ||
+         frame->format() == media::PIXEL_FORMAT_YV12A))) {
     // Since connecting sources and sinks do not check the format, we need to
     // just ignore formats that we can not handle.
     NOTREACHED();
     return;
   }
 
+  // Drop alpha channel since we do not support it yet.
+  if (frame->format() == media::PIXEL_FORMAT_YV12A)
+    frame->DropYV12AAlphaChannel();
+
   // Inject the frame via the VideoFrameFactory of base class.
   MediaVideoFrameFactory* media_video_frame_factory =
       reinterpret_cast<MediaVideoFrameFactory*>(frame_factory());