Reland of: Make OffscreenCanvas Transferable

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

Index: third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp
diff --git a/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp b/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp
index 2979dcbabdb74c80e0c7286a410af02a12fa8a23..a88ff6a5088d18410dcb489605501c3fdb4337e3 100644
--- a/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp
+++ b/third_party/WebKit/Source/modules/offscreencanvas/OffscreenCanvasModules.cpp
@@ -10,8 +10,13 @@
 
 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, "Cannot get context of a neutered OffscreenCanvas");

[Justin Novosad, 2016/04/26 20:08:32]

Message: "OffscreenCanvas object is detached"

[xidachen, 2016/04/26 20:40:59]

Done.

+        return nullptr;
+    }
+
     CanvasRenderingContext* context = offscreenCanvas.getCanvasRenderingContext(id, attributes);
     if (!context)
         return nullptr;