media: Add support for playback of VP8 Alpha video streams

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 3483e9191a91307ebb9bb8253f8fb3becac3ed09..c6b4b36531fdc2ac00cd3abc18b02eef58bc938a 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -22,13 +22,14 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
   };
 
   enum {
-    kMaxPlanes = 3,
+    kMaxPlanes = 4,
 
     kRGBPlane = 0,
 
     kYPlane = 0,
     kUPlane = 1,
     kVPlane = 2,
+    kAPlane = 3,
   };
 
   // Surface formats roughly based on FOURCC labels, see:
@@ -43,6 +44,7 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
     EMPTY = 9,  // An empty frame.
     I420 = 11,  // 12bpp YVU planar 1x1 Y, 2x2 UV samples.
     NATIVE_TEXTURE = 12,  // Native texture.  Pixel-format agnostic.
+    YV12A = 13,  // 20bpp YUVA planar 1x1 Y, 2x2 VU, 1x1 A samples.
   };
 
   // Creates a new frame in system memory with given parameters. Buffers for
@@ -165,6 +167,10 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
   // context.  Calls MD5Update with the context and the contents of the frame.
   void HashFrameForTesting(base::MD5Context* context);
 
+  bool HasAlpha() const {

[scherkus (not reviewing), 2013/02/27 07:28:26]

this method is a bit deceiving

for example ... if format == NATIVE_TEXTURE, it would *seem* that this would be
an OK method to call when in reality it will hit a NOTREACHED().

where is this method used? I actually couldn't find a caller but I could have
skipped over it

[vignesh, 2013/03/28 21:45:12]

sorry, this was a method  i used while debugging. it's not used anywhere now.
removing.

+    return IsValidPlane(kAPlane);
+  }
+
  private:
   friend class base::RefCountedThreadSafe<VideoFrame>;
   // Clients must use the static CreateFrame() method to create a new frame.