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

components/proximity_auth/ble/bluetooth_low_energy_connection_finder.h

 // Copyright 2015 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_PROXIMITY_AUTH_BLE_BLUETOOTH_LOW_ENERGY_CONNECTION_FINDER_H
 #define COMPONENTS_PROXIMITY_AUTH_BLE_BLUETOOTH_LOW_ENERGY_CONNECTION_FINDER_H
 
 #include <set>
 #include <string>
 
@@ skipping 108 matching lines @@
   bool HasService(device::BluetoothDevice* device);
 
   // Restarts the discovery session after creating |connection_| fails.
   void RestartDiscoverySessionWhenReady();
 
   // Used to invoke |connection_callback_| asynchronously, decoupling the
   // callback invocation from the ConnectionObserver callstack.
   void InvokeCallbackAsync();
 
   // Returns the device with |device_address|.
-  device::BluetoothDevice* GetDevice(std::string device_address);
+  device::BluetoothDevice* GetDevice(const std::string& device_address);
 
   // The remote BLE device being searched. It maybe empty, in this case the
   // remote device should advertise |remote_service_uuid_| and
   // |advertised_name_|.
   RemoteDevice remote_device_;
 
   // The uuid of the service it looks for to establish a GattConnection.
   device::BluetoothUUID remote_service_uuid_;
 
   // The finder strategy being used. See |IsRightDevice()|.
@@ skipping 26 matching lines @@
   int max_number_of_tries_;
 
   base::WeakPtrFactory<BluetoothLowEnergyConnectionFinder> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(BluetoothLowEnergyConnectionFinder);
 };
 
 }  // namespace proximity_auth
 
 #endif  // COMPONENTS_PROXIMITY_AUTH_BLE_BLUETOOTH_CONNECTION_FINDER_H