Refactor RenderWidgetHost::set_paint_observer()

chrome/browser/renderer_host/render_widget_host_painting_observer.h

-// Copyright (c) 2009 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 CHROME_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_PAINTING_OBSERVER_H_
-#define CHROME_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_PAINTING_OBSERVER_H_
-#pragma once
-
-class BackingStore;
-class RenderWidgetHost;
-
-namespace gfx {
-class Size;
-}
-
-// This class can be used to observe painting events for a RenderWidgetHost.
-// Its primary goal in Chrome is to allow thumbnails to be generated.
-class RenderWidgetHostPaintingObserver {
- public:
-  // Indicates the RenderWidgetHost is about to destroy the backing store. The
-  // backing store will still be valid when this call is made.
-  virtual void WidgetWillDestroyBackingStore(RenderWidgetHost* widget,
-                                             BackingStore* backing_store) = 0;
-
-  // Indicates that the RenderWidgetHost just updated the backing store.
-  virtual void WidgetDidUpdateBackingStore(RenderWidgetHost* widget) = 0;
-
-  // This notifies the painting observer that a PaintAtSizeACK was
-  // received.
-  virtual void WidgetDidReceivePaintAtSizeAck(
-      RenderWidgetHost* widget,
-      int tag,
-      const gfx::Size& size) = 0;
-
- protected:
-  virtual ~RenderWidgetHostPaintingObserver() {}
-};
-
-#endif  // CHROME_BROWSER_RENDERER_HOST_RENDER_WIDGET_HOST_PAINTING_OBSERVER_H_