Monitor VideoResourceUpdater reusing destructed resource in Debug mode.

cc/resources/video_resource_updater.h

Index: cc/resources/video_resource_updater.h
diff --git a/cc/resources/video_resource_updater.h b/cc/resources/video_resource_updater.h
index 4e11110a01ca1eb89894fe5c775493d0972781f1..df31ff5d5fd3cb9ceb96fca97303d93eef86fcb5 100644
--- a/cc/resources/video_resource_updater.h
+++ b/cc/resources/video_resource_updater.h
@@ -111,7 +111,12 @@ class CC_EXPORT VideoResourceUpdater
                                            const media::VideoFrame* video_frame,
                                            size_t plane_index);
 
-  static void SetPlaneResourceUniqueId(const media::VideoFrame* video_frame,
+  // Side effect: Sets RESOURCE_UPDATER_FLAG boolean in the video frame's
+  // metadata. This is used to prevent reusing the resource in the case that
+  // the original VideoFrame is destroyed and a new VideoFrame is re-created
+  // with the same pointer and the timestamps are all set to zero (or not set)
+  // by the client.

[xhwang, 2016/02/23 17:48:51]

One question: Is it possible to require the timestamp to always be set (and
hopefully they are unique?) so we don't need an extra flag to fix this?

[xjz, 2016/02/23 23:53:15]

It is difficult to check whether the timestamp is correctly set (unique for each
frame) here. If not, the incorrectly reusing of the old resource may happen. And
once it happens, it is difficult to debug. It makes sense to set and check the
status in VideoResourceUpdater.  

+  static void SetPlaneResourceUniqueId(media::VideoFrame* video_frame,
                                        size_t plane_index,
                                        PlaneResource* plane_resource);