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 31fa3eaf232ae0fcb181779ffe66f2b9ab14d0ea..fc5caa7d9c5b4bf1f81e7a62c3f4d56783b277cc 100644
--- a/Source/core/dom/Document.cpp
+++ b/Source/core/dom/Document.cpp
@@ -4948,7 +4948,7 @@ 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, Nullable<RefPtrWillBeRawPtr<CanvasRenderingContext2D> >& context2d, Nullable<RefPtrWillBeRawPtr<WebGLRenderingContext> >& context3d)
 {
     HTMLCanvasElement& element = getCSSCanvasElement(name);
     element.setSize(IntSize(width, height));
@@ -4957,11 +4957,9 @@ void Document::getCSSCanvasContext(const String& type, const String& name, int w
         return;
 
     if (context->is2d()) {
-        is2d = true;
-        context2d = toCanvasRenderingContext2D(context);
+        context2d.set(toCanvasRenderingContext2D(context));
     } else if (context->is3d()) {
-        is3d = true;
-        context3d = toWebGLRenderingContext(context);
+        context3d.set(toWebGLRenderingContext(context));
     }
 }