Made sure FilterEngine instances are always initialized

include/AdblockPlus/FilterEngine.h

 /*
  * This file is part of Adblock Plus <http://adblockplus.org/>,
  * Copyright (C) 2006-2013 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 50 matching lines @@
     Subscription(JsValuePtr value);
   };
 
   typedef std::tr1::shared_ptr<Filter> FilterPtr;
   typedef std::tr1::shared_ptr<Subscription> SubscriptionPtr;
 
   class FilterEngine
   {
   public:
     explicit FilterEngine(JsEnginePtr jsEngine);
-    bool IsInitialized() const;
     FilterPtr GetFilter(const std::string& text);
     SubscriptionPtr GetSubscription(const std::string& url);
     std::vector<FilterPtr> GetListedFilters() const;
     std::vector<SubscriptionPtr> GetListedSubscriptions() const;
     std::vector<SubscriptionPtr> FetchAvailableSubscriptions() const;
     FilterPtr Matches(const std::string& url,
         const std::string& contentType,
         const std::string& documentUrl);
     std::vector<std::string> GetElementHidingSelectors(const std::string& domain) const;
 
   private:
     JsEnginePtr jsEngine;
+    bool initialized;
+
+    void InitDone();
   };
 }
 
 #endif