Issue 3594 - remove circular references JsEngine-JsValue-JsEngine

src/JsContext.h

 /*
  * 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
  * 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/>.
  */
 
 #ifndef ADBLOCK_PLUS_JS_CONTEXT_H
 #define ADBLOCK_PLUS_JS_CONTEXT_H
 
 #include <v8.h>
 #include <AdblockPlus/JsEngine.h>
 
 namespace AdblockPlus
 {
   class JsContext
   {
   public:
-    explicit JsContext(const JsEnginePtr jsEngine);
-
+    explicit JsContext(const std::weak_ptr<JsEngine>& jsEngine);
+    JsEngine& GetJsEngine() {
+      return *jsEngine;
+    }
   private:
+    JsEnginePtr jsEngine;
     const v8::Locker locker;
     const v8::Isolate::Scope isolateScope;
     const v8::HandleScope handleScope;
     const v8::Context::Scope contextScope;
   };
 }
 
 #endif