Make OffscreenCanvas an EventTarget

third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.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 OffscreenCanvasRenderingContext2D_h
 #define OffscreenCanvasRenderingContext2D_h
 
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/html/canvas/CanvasRenderingContextFactory.h"
@@ skipping 66 matching lines @@
   sk_sp<SkImageFilter> stateGetFilter() final;
   void snapshotStateForFilter() final {}
 
   void validateStateStack() const final;
 
   bool hasAlpha() const final { return creationAttributes().alpha(); }
   bool isContextLost() const override;
 
   ImageBitmap* transferToImageBitmap(ScriptState*) final;
 
+  ExecutionContext* getExecutionContext() final {
+    return m_executionContext.get();
+  }
+
  protected:
   OffscreenCanvasRenderingContext2D(
       ScriptState*,
       OffscreenCanvas*,
       const CanvasContextCreationAttributes& attrs);
   DECLARE_VIRTUAL_TRACE();
 
  private:
   bool m_needsMatrixClipRestore = false;
   std::unique_ptr<ImageBuffer> m_imageBuffer;
 
   bool isPaintable() const final;
 
   RefPtr<StaticBitmapImage> transferToStaticBitmapImage();
+
+  Member<ExecutionContext> m_executionContext;
 };
 
 DEFINE_TYPE_CASTS(OffscreenCanvasRenderingContext2D,
                   CanvasRenderingContext,
                   context,
                   context->is2d() && context->getOffscreenCanvas(),
                   context.is2d() && context.getOffscreenCanvas());
 
 }  // namespace blink
 
 #endif  // OffscreenCanvasRenderingContext2D_h