Clean up HID backend and API.

device/hid/hid_service.h

 // Copyright (c) 2014 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 DEVICE_HID_HID_SERVICE_H_
 #define DEVICE_HID_HID_SERVICE_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 22 matching lines @@
  public:
   // Must be called on FILE thread.
   static HidService* GetInstance();
 
   // Enumerates and returns a list of device identifiers.
   virtual void GetDevices(std::vector<HidDeviceInfo>* devices);
 
   // Fills in the device info struct of the given device_id.
   // Returns true if succeed.
   // Returns false if the device_id is invalid, with info untouched.
-  bool GetInfo(std::string device_id, HidDeviceInfo* info) const;
+  bool GetInfo(const std::string& device_id, HidDeviceInfo* info) const;
 
   virtual scoped_refptr<HidConnection> Connect(
-      std::string platform_device_id) = 0;
+      const std::string& device_id) = 0;
 
   // Implements base::MessageLoop::DestructionObserver
   virtual void WillDestroyCurrentMessageLoop() OVERRIDE;
 
   // Gets whether the HidService have been successfully initialized.
   bool initialized() const { return initialized_; }
 
  protected:
   friend class HidServiceContainer;
   friend struct base::DefaultDeleter<HidService>;
   friend class HidConnectionTest;
 
   HidService();
   virtual ~HidService();
 
   static HidService* CreateInstance();
 
   virtual void AddDevice(HidDeviceInfo info);
-  virtual void RemoveDevice(std::string platform_device_id);
+  virtual void RemoveDevice(const std::string& device_id);
 
   typedef std::map<std::string, HidDeviceInfo> DeviceMap;
   DeviceMap devices_;
 
   bool initialized_;
 
   base::ThreadChecker thread_checker_;
 
   DISALLOW_COPY_AND_ASSIGN(HidService);
 };
 
 }  // namespace device
 
 #endif  // DEVICE_HID_HID_SERVICE_H_