Use SkSrc_Mode in SkCanvasVideoRenderer, to prevent transparent video frames from blending with reu…

media/base/video_frame.h

Index: media/base/video_frame.h
diff --git a/media/base/video_frame.h b/media/base/video_frame.h
index 8a607e02cd37e0baeecb459e87ae84ed61bf340d..2445dd1b400d20166232e095caf3ff291e52d0b3 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -189,6 +189,11 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
   // equivalent of RGB(0,0,0).
   static scoped_refptr<VideoFrame> CreateBlackFrame(const gfx::Size& size);
 
+  // Allocates YV12A frame based on |size|, and sets its data to the YUVA
+  // equivalent of RGBA(0,0,0,0).
+  static scoped_refptr<VideoFrame> CreateTransparentFrame(
+      const gfx::Size& size);
+
 #if defined(VIDEO_HOLE)
   // Allocates a hole frame.
   static scoped_refptr<VideoFrame> CreateHoleFrame(const gfx::Size& size);