Monitor VideoResourceUpdater reusing destructed resource in Debug mode.

cc/resources/video_resource_updater.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_RESOURCES_VIDEO_RESOURCE_UPDATER_H_
 #define CC_RESOURCES_VIDEO_RESOURCE_UPDATER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 93 matching lines @@
     PlaneResource(unsigned resource_id,
                   const gfx::Size& resource_size,
                   ResourceFormat resource_format,
                   gpu::Mailbox mailbox);
   };
 
   static bool PlaneResourceMatchesUniqueID(const PlaneResource& plane_resource,
                                            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);
 
   // This needs to be a container where iterators can be erased without
   // invalidating other iterators.
   typedef std::list<PlaneResource> ResourceList;
   ResourceList::iterator AllocateResource(const gfx::Size& plane_size,
                                           ResourceFormat format,
                                           bool has_mailbox,
                                           bool immutable_hint);
@@ skipping 26 matching lines @@
   // Recycle resources so that we can reduce the number of allocations and
   // data transfers.
   ResourceList all_resources_;
 
   DISALLOW_COPY_AND_ASSIGN(VideoResourceUpdater);
 };
 
 }  // namespace cc
 
 #endif  // CC_RESOURCES_VIDEO_RESOURCE_UPDATER_H_