[Android O] Refactor channel initialization

chrome/android/java/src/org/chromium/chrome/browser/notifications/NotificationManagerProxy.java

 // 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.
 
 package org.chromium.chrome.browser.notifications;
 
 import android.app.Notification;
 
 /**
  * A proxy for the Android Notification Manager. This allows tests to be written without having to
  * use the real Notification Manager.
  *
  * @see http://developer.android.com/reference/android/app/NotificationManager.html
  */
 public interface NotificationManagerProxy {
     void cancel(int id);
     void cancel(String tag, int id);
     void cancelAll();
+    void createNotificationChannel(ChannelsInitializer.Channel channel);
+    void createNotificationChannelGroup(ChannelsInitializer.ChannelGroup channelGroup);
+
     void notify(int id, Notification notification);
     void notify(String tag, int id, Notification notification);
 }