exo::CompositorFrameSinkHolder's release callbacks hold ref

components/exo/compositor_frame_sink_holder.h

 // Copyright 2016 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 COMPONENTS_EXO_COMPOSITOR_FRAME_SINK_HOLDER_H_
 #define COMPONENTS_EXO_COMPOSITOR_FRAME_SINK_HOLDER_H_
 
 #include <list>
 #include <map>
 #include <memory>
@@ skipping 61 matching lines @@
   // Overridden from SurfaceObserver:
   void OnSurfaceDestroying(Surface* surface) override;
 
  private:
   friend class base::RefCounted<CompositorFrameSinkHolder>;
 
   ~CompositorFrameSinkHolder() override;
 
   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_;
   std::unique_ptr<CompositorFrameSink> frame_sink_;
 
   std::list<FrameCallback> active_frame_callbacks_;
   std::unique_ptr<cc::ExternalBeginFrameSource> begin_frame_source_;
   bool needs_begin_frame_ = false;
   cc::BeginFrameArgs last_begin_frame_args_;
   mojo::Binding<cc::mojom::MojoCompositorFrameSinkClient> binding_;
 
   base::WeakPtrFactory<CompositorFrameSinkHolder> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(CompositorFrameSinkHolder);
 };
 
 }  // namespace exo
 
 #endif  // COMPONENTS_EXO_COMPOSITOR_FRAME_SINK_HOLDER_H_