Make OffscreenCanvas an EventTarget

third_party/WebKit/Source/core/html/canvas/CanvasRenderingContext.h

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 158 matching lines @@
 
   bool wouldTaintOrigin(CanvasImageSource*, SecurityOrigin* = nullptr);
   void didMoveToNewDocument(Document*);
 
   void detachCanvas() { m_canvas = nullptr; }
 
   const CanvasContextCreationAttributes& creationAttributes() const {
     return m_creationAttributes;
   }
 
+  // This method should be called on OffscreenCanvas's context only.
+  virtual ExecutionContext* getExecutionContext() {
+    NOTREACHED();
+    return nullptr;
+  }
+
  protected:
   CanvasRenderingContext(HTMLCanvasElement*,
                          OffscreenCanvas*,
                          const CanvasContextCreationAttributes&);
   DECLARE_VIRTUAL_TRACE();
   virtual void stop() = 0;
 
  private:
   void dispose();
 
   Member<HTMLCanvasElement> m_canvas;
   Member<OffscreenCanvas> m_offscreenCanvas;
   HashSet<String> m_cleanURLs;
   HashSet<String> m_dirtyURLs;
   CanvasColorSpace m_colorSpace;
   CanvasContextCreationAttributes m_creationAttributes;
 };
 
 }  // namespace blink
 
 #endif