Make OffscreenCanvas an EventTarget

third_party/WebKit/Source/core/offscreencanvas/OffscreenCanvas.cpp

 // Copyright 2015 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.
 
 #include "core/offscreencanvas/OffscreenCanvas.h"
 
 #include "core/dom/ExceptionCode.h"
 #include "core/fileapi/Blob.h"
 #include "core/html/ImageData.h"
 #include "core/html/canvas/CanvasAsyncBlobCreator.h"
@@ skipping 221 matching lines @@
       imageData->data(), encodingMimeType, imageData->size(), startTime,
       document, resolver);
 
   asyncCreator->scheduleAsyncBlobCreation(options.quality());
 
   return resolver->promise();
 }
 
 DEFINE_TRACE(OffscreenCanvas) {
   visitor->trace(m_context);
+  visitor->trace(m_executionContext);
+  EventTarget::trace(visitor);
 }
 
 }  // namespace blink