Have Document::getCSSCanvasElement() return a reference

Source/core/dom/Document.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
@@ skipping 824 matching lines @@
     Vector<IconURL> iconURLs(int iconTypesMask);
 
     void setUseSecureKeyboardEntryWhenActive(bool);
     bool useSecureKeyboardEntryWhenActive() const;
 
     void updateFocusAppearanceSoon(bool restorePreviousSelection);
     void cancelFocusAppearanceUpdate();
 
     // 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&);
 
     // FIXME(crbug.com/305497): This should be removed once DOMWindow is an ExecutionContext.
     virtual void postTask(PassOwnPtr<ExecutionContextTask>) OVERRIDE; // Executes the task on context's thread asynchronously.
 
     virtual void tasksWereSuspended() OVERRIDE FINAL;
     virtual void tasksWereResumed() OVERRIDE FINAL;
     virtual void suspendScheduledTasks() OVERRIDE FINAL;
@@ skipping 540 matching lines @@
 inline bool Node::isDocumentNode() const
 {
     return this == document();
 }
 
 Node* eventTargetNodeForDocument(Document*);
 
 } // namespace WebCore
 
 #endif // Document_h