bluetooth: Blink-side implementation of getCharacteristic.

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://webbluetoothcg.github.io/web-bluetooth/#idl-def-bluetoothgattcharacteristic
 
 // Implement BluetoothGATTCharacteristic interface: https://crbug.com/483344
 typedef DOMString UUID;
 
 [
     GarbageCollected,
     RuntimeEnabled=WebBluetooth,
 ] interface BluetoothGATTCharacteristic {//: CharacteristicEventHandlers {
     // readonly    attribute BluetoothGATTService     service;
-    // readonly    attribute UUID                     uuid;
+    readonly    attribute UUID                     uuid;
     // readonly    attribute CharacteristicProperties properties;
     // readonly    attribute ArrayBuffer?             value;
     // Promise<BluetoothGATTDescriptor>           getDescriptor(BluetoothDescriptorUUID descriptor);
     // Promise<sequence<BluetoothGATTDescriptor>> getDescriptors(optional BluetoothDescriptorUUID descriptor);
     // Promise<ArrayBuffer>                       readValue();
     // Promise<void>                              writeValue(BufferSource value);
     // Promise<void>                              startNotifications();
     // Promise<void>                              stopNotifications();
 };