Reland of: Make OffscreenCanvas Transferable

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/html/canvas/CanvasContextCreationAttributes.h"
 #include "core/html/canvas/CanvasRenderingContext.h"
 #include "core/html/canvas/CanvasRenderingContextFactory.h"
@@ skipping 14 matching lines @@
 void OffscreenCanvas::setWidth(unsigned width)
 {
     m_size.setWidth(clampTo<int>(width));
 }
 
 void OffscreenCanvas::setHeight(unsigned height)
 {
     m_size.setHeight(clampTo<int>(height));
 }
 
+void OffscreenCanvas::setNeutered()
+{
+    ASSERT(!m_context);
+    m_isNeutered = true;
+    m_size.setWidth(0);
+    m_size.setHeight(0);
+}
+
 ImageBitmap* OffscreenCanvas::transferToImageBitmap(ExceptionState& exceptionState)
 {
+    if (m_isNeutered) {
+        exceptionState.throwDOMException(InvalidStateError, "Cannot transfer an ImageBitmap from a detached OffscreenCanvas");
+        return nullptr;
+    }
     if (!m_context) {
         exceptionState.throwDOMException(InvalidStateError, "Cannot transfer an ImageBitmap from an OffscreenCanvas with no context");
         return nullptr;
     }
     ImageBitmap* image = m_context->transferToImageBitmap(exceptionState);
     if (!image) {
         // Undocumented exception (not in spec)
         exceptionState.throwDOMException(V8GeneralError, "Out of memory");
     }
     return image;
@@ skipping 39 matching lines @@
 {
     CanvasRenderingContext::ContextType type = renderingContextFactory->getContextType();
     ASSERT(type < CanvasRenderingContext::ContextTypeCount);
     ASSERT(!renderingContextFactories()[type]);
     renderingContextFactories()[type] = renderingContextFactory;
 }
 
 DEFINE_TRACE(OffscreenCanvas)
 {
     visitor->trace(m_context);
-    visitor->trace(m_canvas);
 }
 
 } // namespace blink