Notify listeners on OffScreenCanvas changes

third_party/WebKit/Source/platform/graphics/OffscreenCanvasPlaceholder.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 OffscreenCanvasPlaceholder_h
 #define OffscreenCanvasPlaceholder_h
 
 #include "platform/PlatformExport.h"
 #include "wtf/RefPtr.h"
 #include "wtf/WeakPtr.h"
 #include <memory>
 
 namespace blink {
 
 class OffscreenCanvasFrameDispatcher;
 class StaticBitmapImage;
 class WebTaskRunner;
 
 class PLATFORM_EXPORT OffscreenCanvasPlaceholder {
  public:
   ~OffscreenCanvasPlaceholder();
 
-  void setPlaceholderFrame(RefPtr<StaticBitmapImage>,
-                           WeakPtr<OffscreenCanvasFrameDispatcher>,
-                           RefPtr<WebTaskRunner>,
-                           unsigned resourceId);
+  virtual void setPlaceholderFrame(RefPtr<StaticBitmapImage>,
+                                   WeakPtr<OffscreenCanvasFrameDispatcher>,
+                                   RefPtr<WebTaskRunner>,
+                                   unsigned resourceId);
   void releasePlaceholderFrame();
 
   static OffscreenCanvasPlaceholder* getPlaceholderById(unsigned placeholderId);
 
   void registerPlaceholder(unsigned placeholderId);
   void unregisterPlaceholder();
   const RefPtr<StaticBitmapImage>& placeholderFrame() const {
     return m_placeholderFrame;
   }
 
  private:
   bool isPlaceholderRegistered() const {
     return m_placeholderId != kNoPlaceholderId;
   }
 
   RefPtr<StaticBitmapImage> m_placeholderFrame;
   WeakPtr<OffscreenCanvasFrameDispatcher> m_frameDispatcher;
   RefPtr<WebTaskRunner> m_frameDispatcherTaskRunner;
   unsigned m_placeholderFrameResourceId = 0;
 
   enum {
     kNoPlaceholderId = -1,
   };
   int m_placeholderId = kNoPlaceholderId;
 };
 
 }  // blink
 
 #endif