Implement the gattserverdisconnected event.

third_party/WebKit/public/platform/modules/bluetooth/web_bluetooth.mojom

 // Copyright 2016 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.
 
 module blink.mojom;
 
 // Errors that can occur during Web Bluetooth execution, which are transformed
 // to a DOMException in Source/modules/bluetooth/BluetoothError.cpp.
 //
 // These errors all produce constant message strings. If a particular message
@@ skipping 142 matching lines @@
   RemoteCharacteristicStopNotifications(
     string characteristic_instance_id) => ();
 };
 
 // Classes should implement this interface and pass an associated pointer
 // bound to them to the WebBluetoothService by using SetClient. Classes
 // that do this will be notified of device events e.g. device disconnection.
 interface WebBluetoothServiceClient {
   RemoteCharacteristicValueChanged(string characteristic_instance_id,
                                    array<uint8> value);
+  GattServerDisconnected(string device_id);
 };