Have Document::getCSSCanvasElement() return a reference

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 c895725783d710aa74c21a8c291e882ea0cd6c36..33c88299609f8d64710cc6644dace1646fda609e 100644
--- a/Source/core/dom/Document.h
+++ b/Source/core/dom/Document.h
@@ -842,7 +842,7 @@ public:
 
     // Extension for manipulating canvas drawing contexts for use in CSS
     CanvasRenderingContext* getCSSCanvasContext(const String& type, const String& name, int width, int height);
-    HTMLCanvasElement* getCSSCanvasElement(const String& name);
+    HTMLCanvasElement& getCSSCanvasElement(const String& name);
 
     bool isDNSPrefetchEnabled() const { return m_isDNSPrefetchEnabled; }
     void parseDNSPrefetchControlHeader(const String&);