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

components/sync_driver/device_info.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_SYNC_DRIVER_DEVICE_INFO_H_
 #define COMPONENTS_SYNC_DRIVER_DEVICE_INFO_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 50 matching lines @@
   // Gets the device type in string form.
   std::string GetDeviceTypeString() const;
 
   // Compares this object's fields with another's.
   bool Equals(const DeviceInfo& other) const;
 
   // Apps can set ids for a device that is meaningful to them but
   // not unique enough so the user can be tracked. Exposing |guid|
   // would lead to a stable unique id for a device which can potentially
   // be used for tracking.
-  void set_public_id(std::string id);
+  void set_public_id(const std::string& id);
 
   // Converts the |DeviceInfo| values to a JS friendly DictionaryValue,
   // which extension APIs can expose to third party apps.
   base::DictionaryValue* ToValue();
 
  private:
   const std::string guid_;
 
   const std::string client_name_;
 
@@ skipping 10 matching lines @@
   // ids in that the same device will have different id for different apps
   // and they are also reset when app/extension is uninstalled.
   std::string public_id_;
 
   DISALLOW_COPY_AND_ASSIGN(DeviceInfo);
 };
 
 }  // namespace sync_driver
 
 #endif  // COMPONENTS_SYNC_DRIVER_DEVICE_INFO_H_