Make OffscreenCanvas an EventTarget

third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h

Index: third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h
diff --git a/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h b/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h
index 3bfa207a8a034fa6d7e3630c66d0d057035917ee..f239d2c35d204228f15f2c82a1c6b0a55a812f52 100644
--- a/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h
+++ b/third_party/WebKit/Source/modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h
@@ -84,6 +84,10 @@ class MODULES_EXPORT OffscreenCanvasRenderingContext2D final
 
   ImageBitmap* transferToImageBitmap(ScriptState*) final;
 
+  ExecutionContext* getExecutionContext() final {
+    return m_executionContext.get();
+  }
+
  protected:
   OffscreenCanvasRenderingContext2D(
       ScriptState*,
@@ -98,6 +102,8 @@ class MODULES_EXPORT OffscreenCanvasRenderingContext2D final
   bool isPaintable() const final;
 
   RefPtr<StaticBitmapImage> transferToStaticBitmapImage();
+
+  Member<ExecutionContext> m_executionContext;
 };
 
 DEFINE_TYPE_CASTS(OffscreenCanvasRenderingContext2D,