Coverity: Fix a few pass-by-values.

chrome/browser/autofill/autofill_external_delegate.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_AUTOFILL_AUTOFILL_EXTERNAL_DELEGATE_H_
 #define CHROME_BROWSER_AUTOFILL_AUTOFILL_EXTERNAL_DELEGATE_H_
 #pragma once
 
 #include <vector>
 
@@ skipping 44 matching lines @@
       const std::vector<string16>& autofill_values,
       const std::vector<string16>& autofill_labels,
       const std::vector<string16>& autofill_icons,
       const std::vector<int>& autofill_unique_ids);
 
   // Inform the delegate that the text field editing has ended, this is
   // used to help record the metrics of when a new popup is shown.
   void DidEndTextFieldEditing();
 
   // Inform the delegate that an autofill suggestion have been chosen.
-  void DidAcceptAutofillSuggestions(string16 value,
+  void DidAcceptAutofillSuggestions(const string16& value,
                                     int unique_id,
                                     unsigned index);
 
   // Informs the delegate that the Autofill previewed form should be cleared.
   virtual void ClearPreviewedForm();
 
   // Hide the Autofill poup.
   virtual void HideAutofillPopup();
 
   // Platforms that wish to implement an external Autofill delegate
@@ skipping 53 matching lines @@
   // The menu index of the "Clear" menu item.
   int suggestions_clear_index_;
 
   // The menu index of the "Autofill options..." menu item.
   int suggestions_options_index_;
 
   DISALLOW_COPY_AND_ASSIGN(AutofillExternalDelegate);
 };
 
 #endif  // CHROME_BROWSER_AUTOFILL_AUTOFILL_EXTERNAL_DELEGATE_H_