IDL: Use Nullable for union type return value

Source/core/dom/Document.h

Index: Source/core/dom/Document.h
diff --git a/Source/core/dom/Document.h b/Source/core/dom/Document.h
index 6cd404bd764209b43a22f842acd0932f2d4ed210..23d57f28fe3a14200af8d53ea03717df98b12458 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -29,6 +29,7 @@
 #define Document_h
 
 #include "bindings/core/v8/ExceptionStatePlaceholder.h"
+#include "bindings/core/v8/Nullable.h"
 #include "bindings/core/v8/ScriptValue.h"
 #include "core/animation/AnimationClock.h"
 #include "core/animation/CompositorPendingAnimations.h"
@@ -836,7 +837,7 @@ public:
     void cancelFocusAppearanceUpdate();
 
     // Extension for manipulating canvas drawing contexts for use in CSS
-    void getCSSCanvasContext(const String& type, const String& name, int width, int height, bool&, RefPtrWillBeRawPtr<CanvasRenderingContext2D>&, bool&, RefPtrWillBeRawPtr<WebGLRenderingContext>&);
+    void getCSSCanvasContext(const String& type, const String& name, int width, int height, Nullable<RefPtrWillBeRawPtr<CanvasRenderingContext2D> >&, Nullable<RefPtrWillBeRawPtr<WebGLRenderingContext> >&);
     HTMLCanvasElement& getCSSCanvasElement(const String& name);
 
     bool isDNSPrefetchEnabled() const { return m_isDNSPrefetchEnabled; }