Reland of: Make OffscreenCanvas Transferable

third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp

 // 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.
 
 #include "modules/offscreencanvas/OffscreenCanvasModules.h"
 
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/offscreencanvas/OffscreenCanvas.h"
 #include "modules/offscreencanvas2d/OffscreenCanvasRenderingContext2D.h"
 
 namespace blink {
 
-OffscreenCanvasRenderingContext2D* OffscreenCanvasModules::getContext(OffscreenCanvas& offscreenCanvas, const String& id, const CanvasContextCreationAttributes& attributes)
+OffscreenCanvasRenderingContext2D* OffscreenCanvasModules::getContext(OffscreenCanvas& offscreenCanvas, const String& id, const CanvasContextCreationAttributes& attributes, ExceptionState& exceptionState)
 {
+    if (offscreenCanvas.isNeutered()) {
+        exceptionState.throwDOMException(InvalidStateError, "OffscreenCanvas object is detached");
+        return nullptr;
+    }
+
     CanvasRenderingContext* context = offscreenCanvas.getCanvasRenderingContext(id, attributes);
     if (!context)
         return nullptr;
 
     return static_cast<OffscreenCanvasRenderingContext2D*>(context);
 }
 
 } // namespace blink