Issue 6859 - Create special subscription group for snippet filters

lib/subscriptionClasses.js

Index: lib/subscriptionClasses.js
===================================================================
--- a/lib/subscriptionClasses.js
+++ b/lib/subscriptionClasses.js
@@ -17,17 +17,18 @@
 
 "use strict";
 
 /**
  * @fileOverview Definition of Subscription class and its subclasses.
  */
 
 const {ActiveFilter, BlockingFilter,
-       WhitelistFilter, ElemHideBase} = require("./filterClasses");
+       WhitelistFilter, ElemHideBase,
+       SnippetFilter} = require("./filterClasses");
 const {FilterNotifier} = require("./filterNotifier");
 const {extend} = require("./coreUtils");
 
 /**
  * Abstract base class for filter subscriptions
  *
  * @param {string} url    download location of the subscription
  * @param {string} [title]  title of the filter subscription
@@ -298,17 +299,18 @@
     if (this._lastDownload)
       buffer.push("lastDownload=" + this._lastDownload);
   }
 });
 
 SpecialSubscription.defaultsMap = new Map([
   ["whitelist", WhitelistFilter],
   ["blocking", BlockingFilter],
-  ["elemhide", ElemHideBase]
+  ["elemhide", ElemHideBase],
+  ["snippet", SnippetFilter]
 ]);
 
 /**
  * Creates a new user-defined filter group.
  * @param {string} [title]  title of the new filter group
  * @return {SpecialSubscription}
  */
 SpecialSubscription.create = function(title)