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..14291d6e85b557772c5dea0c1116c1b7d26b71d9 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;

[Daniel Erat, 2015/09/21 14:12:45]

this makes me nervous. if one of the methods called below deletes this entry
from device_map_, then the reference will become invalid and there's the
potential for a use-after-free. i'd prefer that you kept the copy here.

[stevenjb, 2015/09/22 01:16:11]

+1. For this kind of minor optimization cleanup I would really prefer to error
on the side of being overly cautious.

[ki.stfu, 2015/09/23 17:36:05]

Done.

       if (FoundDevice(device_id, connecting_devices_, NULL))
         return;
       UpdateClickedDevice(device_id, sender);