Issue 6916 - Encapsulate filter subscriptions

lib/filterClasses.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 56 matching lines @@
     throw new Error("Please define filter type in the subclass");
   },
 
   /**
    * Yields subscriptions to which the filter belongs.
    * @yields {Subscription}
    */
   *subscriptions()
   {
     yield* this._subscriptions;
+  },
+
+  /**
+   * The number of subscriptions to which the filter belongs.
+   * @type {number}
+   */
+  get subscriptionCount()
+  {
+    return this._subscriptions.size;
   },
 
   /**
    * Adds a subscription to the set of subscriptions to which the filter
    * belongs.
    * @param {Subscription} subscription
    */
   addSubscription(subscription)
   {
     this._subscriptions.add(subscription);
@@ skipping 1119 matching lines @@
 
   /**
    * Script that should be executed
    * @type {string}
    */
   get script()
   {
     return this.body;
   }
 });