exo::CompositorFrameSinkHolder's release callbacks hold ref

components/exo/compositor_frame_sink_holder.h

Index: components/exo/compositor_frame_sink_holder.h
diff --git a/components/exo/compositor_frame_sink_holder.h b/components/exo/compositor_frame_sink_holder.h
index 59cc9879e8908be5adeeae3adf1a92fa5b83bd4c..c5f75eb6f1fe12ff82dcc08061228d44ecf275fb 100644
--- a/components/exo/compositor_frame_sink_holder.h
+++ b/components/exo/compositor_frame_sink_holder.h
@@ -79,14 +79,9 @@ class CompositorFrameSinkHolder
 
   void UpdateNeedsBeginFrame();
 
-  // Each release callback holds a reference to the CompositorFrameSinkHolder
-  // itself to keep it alive. Running and erasing the callbacks might result in
-  // the instance being destroyed. Therefore, we should not access any member
-  // variables after running and erasing the callbacks.
+  // A collection of callbacks used to release resources.
   using ResourceReleaseCallbackMap =
-      std::map<int,
-               std::pair<scoped_refptr<CompositorFrameSinkHolder>,
-                         std::unique_ptr<cc::SingleReleaseCallback>>>;
+      std::map<int, std::unique_ptr<cc::SingleReleaseCallback>>;

[reveman, 2017/01/02 19:57:56]

Do we need to replace the use of cc::SingleReleaseCallback with a simple
base::Callback to allow it to not run when the buffer is destroyed? I think the
DCHECK in cc::SingleReleaseCallback dtor will fail otherwise.

   ResourceReleaseCallbackMap release_callbacks_;
 
   Surface* surface_;