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

Source/core/inspector/InspectorPageAgent.cpp

 /*
  * 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 881 matching lines @@
 }
 
 Frame* InspectorPageAgent::assertFrame(ErrorString* errorString, const String& frameId)
 {
     Frame* frame = frameForId(frameId);
     if (!frame)
         *errorString = "No frame for given id found";
     return frame;
 }
 
-String InspectorPageAgent::resourceSourceMapURL(const String& url)
+const AtomicString& InspectorPageAgent::resourceSourceMapURL(const String& url)
 {
-    DEFINE_STATIC_LOCAL(String, sourceMapHttpHeader, ("SourceMap"));
-    DEFINE_STATIC_LOCAL(String, deprecatedSourceMapHttpHeader, ("X-SourceMap"));
+    DEFINE_STATIC_LOCAL(const AtomicString, sourceMapHttpHeader, ("SourceMap", AtomicString::ConstructFromLiteral));
+    DEFINE_STATIC_LOCAL(const AtomicString, deprecatedSourceMapHttpHeader, ("X-SourceMap", AtomicString::ConstructFromLiteral));
     if (url.isEmpty())
-        return String();
+        return nullAtom;
     Frame* frame = mainFrame();
     if (!frame)
-        return String();
+        return nullAtom;
     Resource* resource = cachedResource(frame, KURL(ParsedURLString, url));
     if (!resource)
-        return String();
-    String deprecatedHeaderSourceMapURL = resource->response().httpHeaderField(deprecatedSourceMapHttpHeader);
+        return nullAtom;
+    const AtomicString& deprecatedHeaderSourceMapURL = resource->response().httpHeaderField(deprecatedSourceMapHttpHeader);
     if (!deprecatedHeaderSourceMapURL.isEmpty()) {
         // FIXME: add deprecated console message here.
         return deprecatedHeaderSourceMapURL;
     }
     return resource->response().httpHeaderField(sourceMapHttpHeader);
 }
 
 bool InspectorPageAgent::deviceMetricsOverrideEnabled()
 {
     return m_enabled && m_deviceMetricsOverridden;
@@ skipping 324 matching lines @@
 }
 
 void InspectorPageAgent::setShowViewportSizeOnResize(ErrorString*, bool show, const bool* showGrid)
 {
     m_state->setBoolean(PageAgentState::showSizeOnResize, show);
     m_state->setBoolean(PageAgentState::showGridOnResize, showGrid && *showGrid);
 }
 
 } // namespace WebCore