media: Implement zero-copy video playback for VP8.

cc/layers/video_layer_impl.cc

Index: cc/layers/video_layer_impl.cc
diff --git a/cc/layers/video_layer_impl.cc b/cc/layers/video_layer_impl.cc
index f22860c746c8b050a6e23fb7f4f343e80af9617c..e8abac783cf44aca219552d1b4d27f5db0809531 100644
--- a/cc/layers/video_layer_impl.cc
+++ b/cc/layers/video_layer_impl.cc
@@ -250,8 +250,15 @@ void VideoLayerImpl::AppendQuads(RenderPass* render_pass,
           frame_->format(), media::VideoFrame::kUPlane, coded_size);
 
       if (frame_->HasTextures()) {
-        DCHECK_EQ(media::PIXEL_FORMAT_I420, frame_->format());
-        DCHECK_EQ(3u, frame_resources_.size());  // Alpha is not supported yet.
+        if (DCHECK_IS_ON()) {
+          if (frame_->format() == media::PIXEL_FORMAT_I420) {
+            DCHECK_EQ(3u, frame_resources_.size());
+          } else if (frame_->format() == media::PIXEL_FORMAT_YV12A) {
+            DCHECK_EQ(4u, frame_resources_.size());
+          } else {
+            NOTREACHED();
+          }
+        }
       } else {
         DCHECK(uv_tex_size ==
                media::VideoFrame::PlaneSize(