Cleanup: Pass std::string as const reference from device/

device/bluetooth/bluetooth_adapter_profile_chromeos_unittest.cc

Index: device/bluetooth/bluetooth_adapter_profile_chromeos_unittest.cc
diff --git a/device/bluetooth/bluetooth_adapter_profile_chromeos_unittest.cc b/device/bluetooth/bluetooth_adapter_profile_chromeos_unittest.cc
index f5b96f817408e39c3c6c51a7dd1d7e7de3c687d6..1b9c0b32a683977bbe13ac69526a9a2e0b5c64b7 100644
--- a/device/bluetooth/bluetooth_adapter_profile_chromeos_unittest.cc
+++ b/device/bluetooth/bluetooth_adapter_profile_chromeos_unittest.cc
@@ -74,7 +74,7 @@ class BluetoothAdapterProfileChromeOSTest : public testing::Test {
   class FakeDelegate
       : public chromeos::BluetoothProfileServiceProvider::Delegate {
    public:
-    FakeDelegate(std::string device_path) : connections_(0) {
+    FakeDelegate(const std::string& device_path) : connections_(0) {
       device_path_ = dbus::ObjectPath(device_path);
     }