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

Source/core/inspector/InspectorPageAgent.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 156 matching lines @@
     Page* page() { return m_page; }
     Frame* mainFrame();
     String createIdentifier();
     Frame* frameForId(const String& frameId);
     String frameId(Frame*);
     bool hasIdForFrame(Frame*) const;
     String loaderId(DocumentLoader*);
     Frame* findFrameWithSecurityOrigin(const String& originRawString);
     Frame* assertFrame(ErrorString*, const String& frameId);
     String scriptPreprocessorSource() { return m_scriptPreprocessorSource; }
-    String resourceSourceMapURL(const String& url);
+    const AtomicString& resourceSourceMapURL(const String& url);
     bool deviceMetricsOverrideEnabled();
     static DocumentLoader* assertDocumentLoader(ErrorString*, Frame*);
 
 private:
     static void resourceContent(ErrorString*, Frame*, const KURL&, String* result, bool* base64Encoded);
 
     InspectorPageAgent(InstrumentingAgents*, Page*, InspectorCompositeState*, InjectedScriptManager*, InspectorClient*, InspectorOverlay*);
     bool deviceMetricsChanged(int width, int height, double deviceScaleFactor, bool emulateViewport, bool fitWindow, double fontScaleFactor, bool textAutosizing);
     void updateViewMetrics(int width, int height, double deviceScaleFactor, bool emulateViewport, bool fitWindow);
     void updateTouchEventEmulationInPage(bool);
@@ skipping 22 matching lines @@
     bool m_deviceMetricsOverridden;
     RefPtr<GeolocationPosition> m_geolocationPosition;
     RefPtr<GeolocationPosition> m_platformGeolocationPosition;
 };
 
 
 } // namespace WebCore
 
 
 #endif // !defined(InspectorPagerAgent_h)