Cleanup: Pass std::string as const reference if possible

components/signin/core/browser/about_signin_internals.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 COMPONENTS_SIGNIN_CORE_BROWSER_ABOUT_SIGNIN_INTERNALS_H_
 #define COMPONENTS_SIGNIN_CORE_BROWSER_ABOUT_SIGNIN_INTERNALS_H_
 
 #include <map>
 #include <string>
 
@@ skipping 55 matching lines @@
   // Each instance of SigninInternalsUI adds itself as an observer to be
   // notified of all updates that AboutSigninInternals receives.
   void AddSigninObserver(Observer* observer);
   void RemoveSigninObserver(Observer* observer);
 
   // Pulls all signin values that have been persisted in the user prefs.
   void RefreshSigninPrefs();
 
   void Initialize(SigninClient* client);
 
-  void OnRefreshTokenReceived(std::string status);
-  void OnAuthenticationResultReceived(std::string status);
+  void OnRefreshTokenReceived(const std::string& status);
+  void OnAuthenticationResultReceived(const std::string& status);
 
   // KeyedService implementation.
   void Shutdown() override;
 
   // Returns a dictionary of values in signin_status_ for use in
   // about:signin-internals. The values are formatted as shown -
   //
   // { "signin_info" :
   //     [ {"title": "Basic Information",
   //        "data": [List of {"label" : "foo-field", "value" : "foo"} elems]
@@ skipping 128 matching lines @@
   // Encapsulates the actual signin and token related values.
   // Most of the values are mirrored in the prefs for persistence.
   SigninStatus signin_status_;
 
   base::ObserverList<Observer> signin_observers_;
 
   DISALLOW_COPY_AND_ASSIGN(AboutSigninInternals);
 };
 
 #endif  // COMPONENTS_SIGNIN_CORE_BROWSER_ABOUT_SIGNIN_INTERNALS_H_