Add flag to signal that video frame must be drawn using an overlay.

media/base/video_frame_metadata.h

Index: media/base/video_frame_metadata.h
diff --git a/media/base/video_frame_metadata.h b/media/base/video_frame_metadata.h
index ce341699752dc9e91901a163569d3699ed7cc9bc..93e593f5d23abb6208a32b1ad9a76502e1f86030 100644
--- a/media/base/video_frame_metadata.h
+++ b/media/base/video_frame_metadata.h
@@ -114,6 +114,10 @@ class MEDIA_EXPORT VideoFrameMetadata {
     // notified about its promotability to an overlay.
     WANTS_PROMOTION_HINT,
 
+    // Windows only: if set, then this frame must be displayed in an overlay

[sandersd (OOO until July 31), 2017/06/13 18:33:35]

FYI: Android has this same situation; frames released to a SurfaceView cannot be
retroactively composited. This hasn't been a huge problem, because we have
written the Android overlay processor to be aware of that. We should probably be
setting this key on Android too, though.

The two keys above (SURFACE_TEXTURE and WANTS_PROMOTION_HINT) are part of the
infrastructure we are building to be able to switch overlay modes in more cases
(that is, other than fullscreen toggle), with the understanding that some frames
may be lost at overlay->composited transitions.

+    // rather than being composited into the framebuffer.
+    REQUIRE_OVERLAY,
+
     NUM_KEYS
   };