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..363aea2c0bd00a7e214cbdcd5bddf91d58918f3a 100644
--- a/components/exo/compositor_frame_sink_holder.h
+++ b/components/exo/compositor_frame_sink_holder.h
@@ -79,14 +79,13 @@ 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.
+  // Each release callback should should take a

[reveman, 2016/12/22 17:00:53]

Isn't this beyond the details of this class? If the callback needs a reference
then it should take it and if not then there's no need to. I think it's better
to explain why a reference is needed at the place where we take that reference.

[Alex Z., 2016/12/22 18:08:48]

Done.

+  // scoped_refptr<CompositorFrameSinkHolder> so that CompositorFrameSinkHolder
+  // lives at least until all callbacks are run. Running the
+  // callbacks might result in the instance being destroyed. Therefore, we
+  // should not access any member variables after running the callbacks.
   using ResourceReleaseCallbackMap =
-      std::map<int,
-               std::pair<scoped_refptr<CompositorFrameSinkHolder>,
-                         std::unique_ptr<cc::SingleReleaseCallback>>>;
+      std::map<int, std::unique_ptr<cc::SingleReleaseCallback>>;
   ResourceReleaseCallbackMap release_callbacks_;
 
   Surface* surface_;