ui: Move compositor/ directory out of gfx/, up to ui/.

ui/gfx/compositor/compositor_observer.h

-// Copyright (c) 2012 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 UI_GFX_COMPOSITOR_COMPOSITOR_OBSERVER_H_
-#define UI_GFX_COMPOSITOR_COMPOSITOR_OBSERVER_H_
-#pragma once
-
-#include "ui/gfx/compositor/compositor_export.h"
-
-namespace ui {
-
-class Compositor;
-
-// A compositor observer is notified when compositing completes.
-class COMPOSITOR_EXPORT CompositorObserver {
- public:
-  // Called when compositing started: it has taken all the layer changes into
-  // account and has issued the graphics commands.
-  virtual void OnCompositingStarted(Compositor* compositor) = 0;
-
-  // Called when compositing completes: the present to screen has completed.
-  virtual void OnCompositingEnded(Compositor* compositor) = 0;
-
- protected:
-  virtual ~CompositorObserver() {}
-};
-
-} // namespace ui
-
-#endif // UI_GFX_COMPOSITOR_COMPOSITOR_OBSERVER_H_