Manage UsbService lifetime in DeviceClient implementations.

device/usb/usb_service_impl.h

 // Copyright 2015 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/usb/usb_service.h"
 
 #include <map>
 #include <queue>
 #include <set>
 
@@ skipping 21 matching lines @@
 typedef struct libusb_context* PlatformUsbContext;
 
 class UsbServiceImpl :
 #if defined(OS_WIN)
     public DeviceMonitorWin::Observer,
 #endif  // OS_WIN
     public UsbService {
  public:
   explicit UsbServiceImpl(
       scoped_refptr<base::SequencedTaskRunner> blocking_task_runner);
+  ~UsbServiceImpl() override;
 
  private:
-  ~UsbServiceImpl() override;
-
   // device::UsbService implementation
   scoped_refptr<UsbDevice> GetDevice(const std::string& guid) override;
   void GetDevices(const GetDevicesCallback& callback) override;
 
 #if defined(OS_WIN)
   // device::DeviceMonitorWin::Observer implementation
   void OnDeviceAdded(const GUID& class_guid,
                      const std::string& device_path) override;
   void OnDeviceRemoved(const GUID& class_guid,
                        const std::string& device_path) override;
@@ skipping 53 matching lines @@
 #if defined(OS_WIN)
   ScopedObserver<DeviceMonitorWin, DeviceMonitorWin::Observer> device_observer_;
 #endif  // OS_WIN
 
   base::WeakPtrFactory<UsbServiceImpl> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(UsbServiceImpl);
 };
 
 }  // namespace device