Have HashMap<KeyType, AtomicString>::get() return a const reference

Source/core/css/StyleSheetContents.cpp

 /*
  * (C) 1999-2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2006, 2007, 2012 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 267 matching lines @@
         return;
     result.iterator->value = uri;
 }
 
 const AtomicString& StyleSheetContents::determineNamespace(const AtomicString& prefix)
 {
     if (prefix.isNull())
         return nullAtom; // No namespace. If an element/attribute has a namespace, we won't match it.
     if (prefix == starAtom)
         return starAtom; // We'll match any namespace.
-    PrefixNamespaceURIMap::const_iterator it = m_namespaces.find(prefix);
-    if (it == m_namespaces.end())
-        return nullAtom;
-    return it->value;
+    return m_namespaces.get(prefix);
 }
 
 void StyleSheetContents::parseAuthorStyleSheet(const CSSStyleSheetResource* cachedStyleSheet, const SecurityOrigin* securityOrigin)
 {
     TRACE_EVENT0("webkit", "StyleSheetContents::parseAuthorStyleSheet");
 
     bool quirksMode = isQuirksModeBehavior(m_parserContext.mode());
 
     bool enforceMIMEType = !quirksMode;
     bool hasValidMIMEType = false;
@@ skipping 244 matching lines @@
     // See the StyleResolver calls in ScopedStyleResolver::addRulesFromSheet.
     for (size_t i = 0; i < m_clients.size(); ++i) {
         if (Document* document = m_clients[i]->ownerDocument())
             document->styleEngine()->clearResolver();
     }
     m_ruleSet.clear();
 }
 
 
 }