compositor: Add protected virtual destructor to CompositorDelegate.

ui/gfx/compositor/compositor.h

 // Copyright (c) 2011 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_H_
 #define UI_GFX_COMPOSITOR_COMPOSITOR_H_
 #pragma once
 
 #include "base/memory/ref_counted.h"
 #include "base/observer_list.h"
@@ skipping 54 matching lines @@
 
  private:
   friend class base::RefCounted<Texture>;
 };
 
 // An interface to allow the compositor to communicate with its owner.
 class COMPOSITOR_EXPORT CompositorDelegate {
  public:
   // Requests the owner to schedule a paint.
   virtual void ScheduleCompositorPaint() = 0;
+
+ protected:
+  virtual ~CompositorDelegate() {}
 };
 
 // Compositor object to take care of GPU painting.
 // A Browser compositor object is responsible for generating the final
 // displayable form of pixels comprising a single widget's contents. It draws an
 // appropriately transformed texture for each transformed view in the widget's
 // view hierarchy.
 class COMPOSITOR_EXPORT Compositor : public base::RefCounted<Compositor> {
  public:
   // Create a compositor from the provided handle.
@@ skipping 68 matching lines @@
   Layer* root_layer_;
 
   ObserverList<CompositorObserver> observer_list_;
 
   friend class base::RefCounted<Compositor>;
 };
 
 }  // namespace ui
 
 #endif  // UI_GFX_COMPOSITOR_COMPOSITOR_H_