Issue 3830 - Add option indicating whether to remove existing filters on raw import

messageResponder.js

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-2016 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 248 matching lines @@
           return;
 
         var seenFilter = Object.create(null);
         for (var i = 0; i < result.filters.length; i++)
         {
           var filter = result.filters[i];
           FilterStorage.addFilter(filter);
           seenFilter[filter.text] = null;
         }
 
+        if (!message.removeExisting)
+          return;
+
         for (var i = 0; i < FilterStorage.subscriptions.length; i++)
         {
           var subscription = FilterStorage.subscriptions[i];
           if (!(subscription instanceof SpecialSubscription))
             continue;
 
           for (var j = subscription.filters.length - 1; j >= 0; j--)
           {
             var filter = subscription.filters[j];
             if (/^@@\|\|([^\/:]+)\^\$document$/.test(filter.text))
@@ skipping 115 matching lines @@
           if (subscription instanceof DownloadableSubscription)
             Synchronizer.execute(subscription, true);
         }
         break;
       case "subscriptions.isDownloading":
         callback(Synchronizer.isExecuting(message.url));
         break;
     }
   });
 })(this);