media: Add support for playback of VP8 Alpha video streams

cc/resources/video_resource_updater.cc

Index: cc/resources/video_resource_updater.cc
diff --git a/cc/resources/video_resource_updater.cc b/cc/resources/video_resource_updater.cc
index a50e4c8b03b5722fc77b14247f6e1c8d5b8f1193..9aa3644f1744699c694928c506c945d097fe5941 100644
--- a/cc/resources/video_resource_updater.cc
+++ b/cc/resources/video_resource_updater.cc
@@ -46,6 +46,7 @@ bool VideoResourceUpdater::VerifyFrame(
   switch (video_frame->format()) {
     // Acceptable inputs.
     case media::VideoFrame::YV12:
+    case media::VideoFrame::YV12A:
     case media::VideoFrame::YV16:
     case media::VideoFrame::NATIVE_TEXTURE:
 #if defined(GOOGLE_TV)
@@ -76,6 +77,7 @@ static gfx::Size SoftwarePlaneDimension(
 
     switch (input_frame_format) {
       case media::VideoFrame::YV12:
+      case media::VideoFrame::YV12A:
         return gfx::ToFlooredSize(gfx::ScaleSize(coded_size, 0.5f, 0.5f));
       case media::VideoFrame::YV16:
         return gfx::ToFlooredSize(gfx::ScaleSize(coded_size, 0.5f, 1.f));
@@ -113,8 +115,10 @@ VideoFrameExternalResources VideoResourceUpdater::CreateForSoftwarePlanes(
 
   // Only YUV software video frames are supported.
   DCHECK(input_frame_format == media::VideoFrame::YV12 ||
+         input_frame_format == media::VideoFrame::YV12A ||
          input_frame_format == media::VideoFrame::YV16);
   if (input_frame_format != media::VideoFrame::YV12 &&
+      input_frame_format != media::VideoFrame::YV12A &&
       input_frame_format != media::VideoFrame::YV16)
     return VideoFrameExternalResources();