Clean up HID backend and API.

device/hid/hid_service.cc

 // 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.
 
 #include "device/hid/hid_service.h"
 
 #include <vector>
 
 #include "base/lazy_instance.h"
 #include "base/logging.h"
@@ skipping 41 matching lines @@
   DCHECK(thread_checker_.CalledOnValidThread());
   STLClearObject(devices);
   for (DeviceMap::iterator it = devices_.begin();
       it != devices_.end();
       ++it) {
     devices->push_back(it->second);
   }
 }
 
 // Fills in the device info struct of the given device_id.
-bool HidService::GetInfo(std::string device_id, HidDeviceInfo* info) const {
+bool HidService::GetInfo(const std::string& device_id,
+                         HidDeviceInfo* info) const {
   DeviceMap::const_iterator it = devices_.find(device_id);
   if (it == devices_.end())
     return false;
   *info = it->second;
   return true;
 }
 
 void HidService::AddDevice(HidDeviceInfo info) {
   if (!ContainsKey(devices_, info.device_id)) {
     DCHECK(thread_checker_.CalledOnValidThread());
     devices_[info.device_id] = info;
   }
 }
 
-void HidService::RemoveDevice(std::string device_id) {
+void HidService::RemoveDevice(const std::string& device_id) {
   if (ContainsKey(devices_, device_id)) {
     DCHECK(thread_checker_.CalledOnValidThread());
     devices_.erase(device_id);
   }
 }
 
 HidService* HidService::CreateInstance() {
 #if defined(OS_LINUX)
     return new HidServiceLinux();
 #elif defined(OS_MACOSX)
     return new HidServiceMac();
 #elif defined(OS_WIN)
     return new HidServiceWin();
 #else
     return NULL;
 #endif
 }
 
 HidService* HidService::GetInstance() {
   if (!g_hid_service_ptr.Get().get()){
     scoped_ptr<HidService> service(CreateInstance());
 
     if (service && service->initialized())
       g_hid_service_ptr.Get().reset(service.release());
   }
   return g_hid_service_ptr.Get().get();
 }
 
 }  // namespace device