IDL: Use Nullable for union type return value

Source/core/dom/Document.cpp

Index: Source/core/dom/Document.cpp
diff --git a/Source/core/dom/Document.cpp b/Source/core/dom/Document.cpp
index 28fea74216df36cc3579a3b75084274ba8398c37..1f309c33979e96fd402b8f48105991100fcf0c9a 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -4945,7 +4945,7 @@ void Document::detachRange(Range* range)
     m_ranges.remove(range);
 }
 
-void Document::getCSSCanvasContext(const String& type, const String& name, int width, int height, bool& is2d, RefPtrWillBeRawPtr<CanvasRenderingContext2D>& context2d, bool& is3d, RefPtrWillBeRawPtr<WebGLRenderingContext>& context3d)
+void Document::getCSSCanvasContext(const String& type, const String& name, int width, int height, RefPtrWillBeRawPtr<CanvasRenderingContext2D>& context2d, RefPtrWillBeRawPtr<WebGLRenderingContext>& context3d)
 {
     HTMLCanvasElement& element = getCSSCanvasElement(name);
     element.setSize(IntSize(width, height));
@@ -4954,10 +4954,8 @@ void Document::getCSSCanvasContext(const String& type, const String& name, int w
         return;
 
     if (context->is2d()) {
-        is2d = true;
         context2d = toCanvasRenderingContext2D(context);
     } else if (context->is3d()) {
-        is3d = true;
         context3d = toWebGLRenderingContext(context);
     }
 }