Cleanup: Pass std::string as const reference from ash/ + minor coding style changes in base/

ash/system/bluetooth/tray_bluetooth.cc

Index: ash/system/bluetooth/tray_bluetooth.cc
diff --git a/ash/system/bluetooth/tray_bluetooth.cc b/ash/system/bluetooth/tray_bluetooth.cc
index c635e10a4edf09d3d780a6e86f0a1a7b8f91ef32..27a3ae836e2f4796919780b7827d0f53bc13c8d1 100644
--- a/ash/system/bluetooth/tray_bluetooth.cc
+++ b/ash/system/bluetooth/tray_bluetooth.cc
@@ -338,7 +338,8 @@ class BluetoothDetailedView : public TrayDetailsView,
 
   // Updates UI of the clicked bluetooth device to show it is being connected
   // or disconnected if such an operation is going to be performed underway.
-  void UpdateClickedDevice(std::string device_id, views::View* item_container) {
+  void UpdateClickedDevice(const std::string& device_id,
+                           views::View* item_container) {
     base::string16 display_name;
     if (FoundDevice(device_id, paired_not_connected_devices_,
                            &display_name)) {
@@ -374,7 +375,7 @@ class BluetoothDetailedView : public TrayDetailsView,
       find = device_map_.find(sender);
       if (find == device_map_.end())
         return;
-      std::string device_id = find->second;
+      const std::string device_id = find->second;
       if (FoundDevice(device_id, connecting_devices_, NULL))
         return;
       UpdateClickedDevice(device_id, sender);