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..6e719b385a0ab9ab7221b6d775f586db7f65fa9d 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_ = release_mailbox_cb;
+}
+
 void VideoFrame::AddDestructionObserver(const base::Closure& callback) {
   DCHECK(!callback.is_null());
   done_callbacks_.push_back(callback);