Replace DeviceManager::GetDeviceChanges with a client interface.

device/usb/mojo/device_manager_impl.h

Index: device/usb/mojo/device_manager_impl.h
diff --git a/device/usb/mojo/device_manager_impl.h b/device/usb/mojo/device_manager_impl.h
index 2334bcddd8ca97f5ce82774e5ff4ecf0987f9c62..2bc524a3f215c23645d5e616a76fc806ea351c8f 100644
--- a/device/usb/mojo/device_manager_impl.h
+++ b/device/usb/mojo/device_manager_impl.h
@@ -53,9 +53,9 @@ class DeviceManagerImpl : public DeviceManager, public UsbService::Observer {
   // DeviceManager implementation:
   void GetDevices(EnumerationOptionsPtr options,
                   const GetDevicesCallback& callback) override;
-  void GetDeviceChanges(const GetDeviceChangesCallback& callback) override;
   void GetDevice(const mojo::String& guid,
                  mojo::InterfaceRequest<Device> device_request) override;
+  void SetClient(DeviceManagerClientPtr client) override;
 
   // Callbacks to handle the async responses from the underlying UsbService.
   void OnGetDevices(EnumerationOptionsPtr options,
@@ -71,16 +71,9 @@ class DeviceManagerImpl : public DeviceManager, public UsbService::Observer {
 
   base::WeakPtr<PermissionProvider> permission_provider_;
 
-  // If there are unfinished calls to GetDeviceChanges their callbacks
-  // are stored in |device_change_callbacks_|. Otherwise device changes
-  // are collected in |devices_added_| and |devices_removed_| until the
-  // next call to GetDeviceChanges.
-  std::queue<GetDeviceChangesCallback> device_change_callbacks_;
-  std::map<std::string, DeviceInfoPtr> devices_added_;
-  std::vector<DeviceInfoPtr> devices_removed_;
-
   UsbService* usb_service_;
   ScopedObserver<UsbService, UsbService::Observer> observer_;
+  DeviceManagerClientPtr client_;
 
   mojo::Closure connection_error_handler_;