Make OffscreenCanvas Transferable

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

Index: third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.cpp
diff --git a/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.cpp b/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.cpp
index 0aedca56e420feed6780983a749a355e6a8f3cd2..435ba369368b3d0818c20fdaa42659c5d45bef5d 100644
--- a/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.cpp
+++ b/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvas.cpp
@@ -35,8 +35,21 @@ void OffscreenCanvas::setHeight(unsigned height)
     m_size.setHeight(clampTo<int>(height));
 }
 
-OffscreenCanvasRenderingContext2D* OffscreenCanvas::getContext(const String& id, const CanvasContextCreationAttributes& attributes)
+void OffscreenCanvas::setNeutered()
 {
+    ASSERT(!m_context);
+    m_isNeutered = true;
+    m_size.setWidth(0);
+    m_size.setHeight(0);
+}
+
+OffscreenCanvasRenderingContext2D* OffscreenCanvas::getContext(const String& id, const CanvasContextCreationAttributes& attributes, ExceptionState& exceptionState)
+{
+    if (m_isNeutered) {
+        exceptionState.throwDOMException(InvalidStateError, "Cannot get context of a neutered OffscreenCanvas");
+        return nullptr;
+    }
+
     OffscreenCanvasRenderingContext::ContextType contextType = OffscreenCanvasRenderingContext::contextTypeFromId(id);
 
     // Unknown type.
@@ -64,6 +77,10 @@ OffscreenCanvasRenderingContext2D* OffscreenCanvas::getContext(const String& id,
 
 ImageBitmap* OffscreenCanvas::transferToImageBitmap(ExceptionState& exceptionState)
 {
+    if (m_isNeutered) {
+        exceptionState.throwDOMException(InvalidStateError, "Cannot transfer an ImageBitmap from a neutered OffscreenCanvas");
+        return nullptr;
+    }
     if (!m_context) {
         exceptionState.throwDOMException(InvalidStateError, "Cannot transfer an ImageBitmap from an OffscreenCanvas with no context");
         return nullptr;
@@ -78,6 +95,7 @@ ImageBitmap* OffscreenCanvas::transferToImageBitmap(ExceptionState& exceptionSta
 
 OffscreenCanvasRenderingContext2D* OffscreenCanvas::renderingContext() const
 {
+    ASSERT(!m_isNeutered);
     // TODO: When there're more than one context type implemented in the future,
     // the return type here should be changed to base class of all Offscreen
     // context types.
@@ -107,7 +125,6 @@ void OffscreenCanvas::registerRenderingContextFactory(PassOwnPtr<OffscreenCanvas
 DEFINE_TRACE(OffscreenCanvas)
 {
     visitor->trace(m_context);
-    visitor->trace(m_canvas);
 }
 
 } // namespace blink