media: Add support for playback of VP8 Alpha video streams

media/base/video_util.cc

Index: media/base/video_util.cc
diff --git a/media/base/video_util.cc b/media/base/video_util.cc
index 4bef0adc88b1e92a17ff0e3e9fe3543ac646fce9..5e2b25f56a83c230efc2f197fc9eb61e91d3b74f 100644
--- a/media/base/video_util.cc
+++ b/media/base/video_util.cc
@@ -61,6 +61,16 @@ void CopyVPlane(const uint8* source, int stride, int rows, VideoFrame* frame) {
   CopyPlane(VideoFrame::kVPlane, source, stride, rows, frame);
 }
 
+void CopyAPlane(const uint8* source, int stride, int rows, VideoFrame* frame) {
+  CopyPlane(VideoFrame::kAPlane, source, stride, rows, frame);
+}
+
+void ClearAPlane(int stride, int rows, VideoFrame *frame) {
+  int rows_to_clear = std::min(frame->rows(VideoFrame::kAPlane), rows);
+  memset(frame->data(VideoFrame::kAPlane), 255,
+         frame->stride(VideoFrame::kAPlane) * rows_to_clear);
+}
+
 void FillYUV(VideoFrame* frame, uint8 y, uint8 u, uint8 v) {
   // Fill the Y plane.
   uint8* y_plane = frame->data(VideoFrame::kYPlane);