Implement WebBluetooth getDescriptor[s]

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

+// 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.
+
+// https://webbluetoothcg.github.io/web-bluetooth/#bluetoothremotegattdescriptor
+
+// Implement BluetoothRemoteGATTDescriptor interface: https://crbug.com/660699
+
+[
+    RuntimeEnabled=WebBluetooth,
+] interface BluetoothRemoteGATTDescriptor  {
+
+    readonly attribute BluetoothRemoteGATTCharacteristic characteristic;
+    readonly attribute UUID                              uuid;
+    readonly attribute DataView?                         value;
+    [CallWith=ScriptState] Promise<DataView>             readValue();
+    [CallWith=ScriptState] Promise<void>                 writeValue(BufferSource value);
+};