bluetooth: Add characteristicvaluechanged event

third_party/WebKit/Source/modules/bluetooth/BluetoothGATTCharacteristic.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://webbluetoothchrome.github.io/web-bluetooth/#idl-def-bluetoothgattcharacteristic
 
 // Implement BluetoothGATTCharacteristic interface: https://crbug.com/483344
 
 [
     GarbageCollected,
     ActiveDOMObject,
     RuntimeEnabled=WebBluetooth,
-] interface BluetoothGATTCharacteristic {//: CharacteristicEventHandlers {
+] interface BluetoothGATTCharacteristic : EventTarget {//: CharacteristicEventHandlers {
     // TODO(ortuno): Add test to make sure service matches the service
     // used to call getCharacteristic.
     // readonly    attribute BluetoothGATTService     service;
     readonly    attribute UUID                   uuid;
     // readonly    attribute CharacteristicProperties properties;
-    // readonly    attribute ArrayBuffer?             value;
+    readonly    attribute ArrayBuffer?             value;
     // Promise<BluetoothGATTDescriptor>           getDescriptor(BluetoothDescriptorUUID descriptor);
     // Promise<sequence<BluetoothGATTDescriptor>> getDescriptors(optional BluetoothDescriptorUUID descriptor);
     [CallWith=ScriptState] Promise<ArrayBuffer> readValue();
     [CallWith=ScriptState] Promise<void>        writeValue(BufferSource value);
     [CallWith=ScriptState] Promise<void>        startNotifications();
     [CallWith=ScriptState] Promise<void>        stopNotifications();
+
+  // TODO(ortuno): Move this to CharacteristicEventHandlers.
+  // http://crbug.com/537459
+  attribute EventHandler oncharacteristicvaluechanged;
 };