Implement BluetoothGattNotifySession::Stop on Android, 2nd attempt

device/bluetooth/bluetooth_gatt_notify_session_mac.mm

-// 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.
-
-#include "device/bluetooth/bluetooth_gatt_notify_session_mac.h"
-
-namespace device {
-BluetoothGattNotifySessionMac::BluetoothGattNotifySessionMac(
-    base::WeakPtr<BluetoothRemoteGattCharacteristicMac> characteristic)
-    : characteristic_(characteristic) {}
-
-BluetoothGattNotifySessionMac::~BluetoothGattNotifySessionMac() {}
-
-std::string BluetoothGattNotifySessionMac::GetCharacteristicIdentifier() const {
-  if (characteristic_.get())
-    return characteristic_->GetIdentifier();
-  return std::string();
-}
-
-bool BluetoothGattNotifySessionMac::IsActive() {
-  return characteristic_.get() != nullptr;
-}
-
-void BluetoothGattNotifySessionMac::Stop(const base::Closure& callback) {
-  NOTIMPLEMENTED();
-}
-
-}  // namespace device