Issue 5137 - [emscripten] Added basic filter storage implementation

lib/filterStorage.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
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
  *
  * You should have received a copy of the GNU General Public License
  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 "use strict";
 
 const {FilterStorage} = require("compiled");
 const {Subscription, SpecialSubscription} = require("subscriptionClasses");
-const {ActiveFilter} = require("filterClasses");
 
 // Backwards compatibility
 FilterStorage.getGroupForFilter = FilterStorage.getSubscriptionForFilter;
 
 /**
  * This property allows iterating over the list of subscriptions. It will delete
  * references automatically at the end of the current loop iteration. If you
  * need persistent references or element access by position you should use
  * FilterStorage.subscriptionAt() instead.
  * @type {Iterable}
  */
 FilterStorage.subscriptions = {
-  [Symbol.iterator]: function*()
+  *[Symbol.iterator]()
   {
     for (let i = 0, l = FilterStorage.subscriptionCount; i < l; i++)
     {
       let subscription = FilterStorage.subscriptionAt(i);
       try
       {
         yield subscription;
       }
       finally
       {
         subscription.delete();
       }
     }
   }
 };
 
 /**
  * Adds a user-defined filter to the most suitable subscription in the list,
  * creates one if none found.
  * @param {Filter} filter
+ * @returns {boolean}
+ *    false if the filter was already in the list and no adding was performed
  */
 FilterStorage.addFilter = function(filter)
 {
   for (let subscription of this.subscriptions)
     if (!subscription.disabled && subscription.indexOfFilter(filter) >= 0)
-      return;
+      return false;
 
   let subscription = this.getSubscriptionForFilter(filter);
   try
   {
     if (!subscription)
     {
       subscription = Subscription.fromURL(null);
       subscription.makeDefaultFor(filter);
       this.addSubscription(subscription);
     }
@@ skipping 23 matching lines @@
         if (index >= 0)
           subscription.removeFilterAt(index);
         else
           break;
       }
     }
   }
 };
 
 exports.FilterStorage = FilterStorage;