Coverity: Fix pass by value error.

chrome/browser/history/url_index_private_data.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 CHROME_BROWSER_HISTORY_URL_INDEX_PRIVATE_DATA_H_
 #define CHROME_BROWSER_HISTORY_URL_INDEX_PRIVATE_DATA_H_
 #pragma once
 
 #include <set>
 #include <string>
@@ skipping 123 matching lines @@
   // candidates may cause perceptible typing response delays in the omnibox.
   // This is likely to occur for short omnibox terms such as 'h' and 'w' which
   // will be found in nearly all history candidates. Results are sorted by
   // descending score. The full results set (i.e. beyond the
   // |kItemsToScoreLimit| limit) will be retained and used for subsequent calls
   // to this function.
   ScoredHistoryMatches HistoryItemsForTerms(const string16& term_string);
 
   // Creates a new URLIndexPrivateData object, populates it from the contents
   // of the cache file stored in |file_path|, and assigns it to |private_data|.
-  // |languages| will be used to break URLs and page titles into words and is
-  // deliberately passed by value.
+  // |languages| will be used to break URLs and page titles into words.
   static void RestoreFromFileTask(
       const FilePath& file_path,
       scoped_refptr<URLIndexPrivateData> private_data,
-      std::string languages);
+      const std::string& languages);
 
   // Constructs a new object by restoring its contents from the file at |path|.
   // Returns the new URLIndexPrivateData which on success will contain the
   // restored data but upon failure will be empty.  |languages| will be used to
   // break URLs and page titles into words
   static scoped_refptr<URLIndexPrivateData> RestoreFromFile(
       const FilePath& path,
       const std::string& languages);
 
   // Constructs a new object by rebuilding its contents from the history
@@ skipping 206 matching lines @@
   // Used for unit testing only. Records the number of candidate history items
   // at three stages in the index searching process.
   size_t pre_filter_item_count_;    // After word index is queried.
   size_t post_filter_item_count_;   // After trimming large result set.
   size_t post_scoring_item_count_;  // After performing final filter/scoring.
 };
 
 }  // namespace history
 
 #endif  // CHROME_BROWSER_HISTORY_URL_INDEX_PRIVATE_DATA_H_