Add mailbox-based Mojo VideoFrame variant.

media/base/video_frame.cc

Index: media/base/video_frame.cc
diff --git a/media/base/video_frame.cc b/media/base/video_frame.cc
index d2808356111d86c56b19644a2f6a51d602c4ca2b..bbb94a9c5983d80e34a8024c35d7be4017c07ea7 100644
--- a/media/base/video_frame.cc
+++ b/media/base/video_frame.cc
@@ -768,6 +768,13 @@ CVPixelBufferRef VideoFrame::cv_pixel_buffer() const {
 }
 #endif
 
+void VideoFrame::SetReleaseMailboxCB(
+    const ReleaseMailboxCB& release_mailbox_cb) {
+  DCHECK(!release_mailbox_cb.is_null());
+  DCHECK(mailbox_holders_release_cb_.is_null());
+  mailbox_holders_release_cb_ = std::move(release_mailbox_cb);

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

OOC nit, not related to your CL: do we need to worry about the thread safty of
VideoFrame?

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

I suppose we do. I added a warning to the header; for now it just says that you
should only call this method in constructor-like situations.

We can fix it with locking if necessary, but we really don't need that for the
current use case.

+}
+
 void VideoFrame::AddDestructionObserver(const base::Closure& callback) {
   DCHECK(!callback.is_null());
   done_callbacks_.push_back(callback);