Add mailbox-based Mojo VideoFrame variant.

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 7ed1162b7a4147956f0d01d95c971ce7bbf4a0ab..47923be7c8662be0ac32d262e5c71f7ad8df9542 100644
--- a/media/base/video_frame.h
+++ b/media/base/video_frame.h
@@ -355,6 +355,11 @@ class MEDIA_EXPORT VideoFrame : public base::RefCountedThreadSafe<VideoFrame> {
   CVPixelBufferRef cv_pixel_buffer() const;
 #endif
 
+  // Sets the mailbox release callback.
+  // The callback may be run from ANY THREAD, and so it is up to the client to
+  // ensure thread safety.
+  void SetReleaseMailboxCB(const ReleaseMailboxCB& release_mailbox_cb);

[sandersd (OOO until July 31), 2017/01/19 19:40:48]

Option B is that the VideoFrame converter needs to become aware of this
callback, and therefore cannot be a standard Mojo converter.

[xhwang, 2017/01/25 18:25:09]

This is fine IMHO. VideoFrame is already a mix of everything :(

[sandersd (OOO until July 31), 2017/01/26 23:49:05]

Acknowledged.

+
   // Adds a callback to be run when the VideoFrame is about to be destroyed.
   // The callback may be run from ANY THREAD, and so it is up to the client to
   // ensure thread safety.  Although read-only access to the members of this