Implement HTMLCanvasElement's transferControlToOffscreen

third_party/WebKit/Source/modules/canvas/HTMLCanvasElementModule.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/canvas/HTMLCanvasElementModule.h"
 
 #include "core/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 
 namespace blink {
 
 void HTMLCanvasElementModule::getContext(HTMLCanvasElement& canvas, const String& type, const CanvasContextCreationAttributes& attributes, RenderingContext& result)
 {
     CanvasRenderingContext* context = canvas.getCanvasRenderingContext(type, attributes);
     if (context) {
         context->setCanvasGetContextResult(result);
     }
 }
 
+OffscreenCanvas* HTMLCanvasElementModule::transferControlToOffscreen(HTMLCanvasElement& canvas, ExceptionState& exceptionState)
+{
+    if (canvas.renderingContext()) {
+        exceptionState.throwDOMException(InvalidStateError, "Cannot transfer control from a canvas that has a rendering context.");
+        return nullptr;
+    }
+    OffscreenCanvas* offscreenCanvas = OffscreenCanvas::create(canvas.width(), canvas.height());
+    offscreenCanvas->setAssociatedCanvas(&canvas);
+    return offscreenCanvas;
 }
+
+}