Have Element::ensureUserAgentShadowRoot() return a reference

Source/core/html/HTMLTextAreaElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2010 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 46 matching lines @@
     void rendererWillBeDestroyed();
 
     void setCols(int);
     void setRows(int);
 
 private:
     HTMLTextAreaElement(const QualifiedName&, Document&, HTMLFormElement*);
 
     enum WrapMethod { NoWrap, SoftWrap, HardWrap };
 
-    virtual void didAddUserAgentShadowRoot(ShadowRoot*) OVERRIDE;
+    virtual void didAddUserAgentShadowRoot(ShadowRoot&) OVERRIDE;
     // FIXME: Author shadows should be allowed
     // https://bugs.webkit.org/show_bug.cgi?id=92608
     virtual bool areAuthorShadowsAllowed() const OVERRIDE { return false; }
 
     void handleBeforeTextInsertedEvent(BeforeTextInsertedEvent*) const;
     static String sanitizeUserInputValue(const String&, unsigned maxLength);
     void updateValue() const;
     void setNonDirtyValue(const String&);
     void setValueCommon(const String&);
 
@@ skipping 57 matching lines @@
 inline bool isHTMLTextAreaElement(const Element* element)
 {
     return element->hasTagName(HTMLNames::textareaTag);
 }
 
 DEFINE_NODE_TYPE_CASTS(HTMLTextAreaElement, hasTagName(HTMLNames::textareaTag));
 
 } //namespace
 
 #endif