Implement WebBluetooth getDescriptor[s]

third_party/WebKit/Source/modules/bluetooth/BluetoothRemoteGATTCharacteristic.idl

 // 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.
 
 // https://webbluetoothcg.github.io/web-bluetooth/#bluetoothremotegattcharacteristic
 
 // Implement BluetoothRemoteGATTCharacteristic interface: https://crbug.com/483344
 
 [
     DependentLifetime,
     RuntimeEnabled=WebBluetooth,
 ] interface BluetoothRemoteGATTCharacteristic : EventTarget {//: CharacteristicEventHandlers {
     readonly attribute BluetoothRemoteGATTService        service;
     readonly attribute UUID                              uuid;
     readonly attribute BluetoothCharacteristicProperties properties;
     readonly attribute DataView?                         value;
-    // Promise<BluetoothRemoteGATTDescriptor>           getDescriptor(BluetoothDescriptorUUID descriptor);
-    // Promise<sequence<BluetoothRemoteGATTDescriptor>> getDescriptors(optional BluetoothDescriptorUUID descriptor);
+    [RaisesException, CallWith=ScriptState] Promise<BluetoothRemoteGATTDescriptor>           getDescriptor(BluetoothDescriptorUUID descriptor);
+    [RaisesException, CallWith=ScriptState] Promise<sequence<BluetoothRemoteGATTDescriptor>> getDescriptors(optional BluetoothDescriptorUUID descriptor);
     [CallWith=ScriptState] Promise<DataView>                          readValue();
     [CallWith=ScriptState] Promise<void>                              writeValue(BufferSource value);
     [CallWith=ScriptState] Promise<BluetoothRemoteGATTCharacteristic> startNotifications();
     [CallWith=ScriptState] Promise<BluetoothRemoteGATTCharacteristic> stopNotifications();
 
     // TODO(ortuno): Move this to CharacteristicEventHandlers.
     // http://crbug.com/537459
     attribute EventHandler oncharacteristicvaluechanged;
 };