Have Element::ensureUserAgentShadowRoot() return a reference

Source/core/html/HTMLMeterElement.cpp

 /*
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 203 matching lines @@
 RenderMeter* HTMLMeterElement::renderMeter() const
 {
     if (renderer() && renderer()->isMeter())
         return toRenderMeter(renderer());
 
     RenderObject* renderObject = userAgentShadowRoot()->firstChild()->renderer();
     ASSERT(!renderObject || renderObject->isMeter());
     return toRenderMeter(renderObject);
 }
 
-void HTMLMeterElement::didAddUserAgentShadowRoot(ShadowRoot* root)
+void HTMLMeterElement::didAddUserAgentShadowRoot(ShadowRoot& root)
 {
     ASSERT(!m_value);
 
     RefPtr<MeterInnerElement> inner = MeterInnerElement::create(document());
-    root->appendChild(inner);
+    root.appendChild(inner);
 
     RefPtr<MeterBarElement> bar = MeterBarElement::create(document());
     m_value = MeterValueElement::create(document());
     m_value->setWidthPercentage(0);
     m_value->updatePseudo();
     bar->appendChild(m_value);
 
     inner->appendChild(bar);
 }
 
 } // namespace