Clean up HID backend and API.

device/hid/hid_service_win.h

Index: device/hid/hid_service_win.h
diff --git a/device/hid/hid_service_win.h b/device/hid/hid_service_win.h
index 428420ed9b0f41e8912afca83166f2b55d782b8e..0c5cfc49d6eef7d0ca28d94a30136ce41aff549b 100644
--- a/device/hid/hid_service_win.h
+++ b/device/hid/hid_service_win.h
@@ -25,14 +25,15 @@ class HidServiceWin : public HidService {
 
   virtual void GetDevices(std::vector<HidDeviceInfo>* devices) OVERRIDE;
 
-  virtual scoped_refptr<HidConnection> Connect(std::string device_id) OVERRIDE;
+  virtual scoped_refptr<HidConnection> Connect(const std::string& device_id)
+      OVERRIDE;
 
  private:
   virtual ~HidServiceWin();
 
   bool Enumerate();
-  void PlatformAddDevice(std::string device_path);
-  void PlatformRemoveDevice(std::string device_path);
+  void PlatformAddDevice(const std::string& device_path);
+  void PlatformRemoveDevice(const std::string& device_path);
 
   DISALLOW_COPY_AND_ASSIGN(HidServiceWin);
 };