Coverity: Fix several pass-by-values.

content/public/browser/web_ui_message_handler.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_PUBLIC_BROWSER_WEB_UI_MESSAGE_HANDLER_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_UI_MESSAGE_HANDLER_H_
 
 #include "base/basictypes.h"
 #include "base/gtest_prod_util.h"
 #include "base/string16.h"
@@ skipping 24 matching lines @@
  protected:
   FRIEND_TEST_ALL_PREFIXES(WebUIMessageHandlerTest, ExtractIntegerValue);
   FRIEND_TEST_ALL_PREFIXES(WebUIMessageHandlerTest, ExtractDoubleValue);
   FRIEND_TEST_ALL_PREFIXES(WebUIMessageHandlerTest, ExtractStringValue);
 
   // Helper methods:
 
   // Adds "url" and "title" keys on incoming dictionary, setting title
   // as the url as a fallback on empty title.
   static void SetURLAndTitle(base::DictionaryValue* dictionary,
-                             string16 title,
+                             const string16& title,
                              const GURL& gurl);
 
   // Extract an integer value from a list Value.
   static bool ExtractIntegerValue(const base::ListValue* value, int* out_int);
 
   // Extract a floating point (double) value from a list Value.
   static bool ExtractDoubleValue(const base::ListValue* value,
                                  double* out_value);
 
   // Extract a string value from a list Value.
@@ skipping 15 matching lines @@
   friend class ::WebUIImpl;
   friend class ::WebUIBrowserTest;
 
   WebUI* web_ui_;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_UI_MESSAGE_HANDLER_H_