Don`t use references to JsEngine to avoid use-after-free errors,switch to shared_ptr instead

include/AdblockPlus/JsEngine.h

 #ifndef ADBLOCKPLUS_JS_ENGINE_H
 #define ADBLOCKPLUS_JS_ENGINE_H
 
 #include <stdexcept>
 #include <string>
 #include <v8.h>
 #include <AdblockPlus/AppInfo.h>
 #include <AdblockPlus/ErrorCallback.h>
 #include <AdblockPlus/FileSystem.h>
 #include <AdblockPlus/JsValue.h>
 #include <AdblockPlus/WebRequest.h>
 
 #include "tr1_memory.h"
 
 namespace AdblockPlus
 {
   class JsError : public std::runtime_error
   {
   public:
     JsError(const v8::Handle<v8::Value> exception,
             const v8::Handle<v8::Message> message);
   };
 
+  class JsEngine;
   typedef std::tr1::shared_ptr<JsEngine> JsEnginePtr;
 
-  class JsEngine
+  class JsEngine : public std::tr1::enable_shared_from_this<JsEngine>
   {
     friend class JsValue;
 
   public:
-    JsEngine(const AppInfo& appInfo = AppInfo());
+    static JsEnginePtr New(const AppInfo& appInfo = AppInfo());
     JsValuePtr Evaluate(const std::string& source,
         const std::string& filename = "");
     void Load(const std::string& scriptPath);
     void Gc();
     JsValuePtr NewValue(const std::string& val);
     JsValuePtr NewValue(int64_t val);
     JsValuePtr NewValue(bool val);
     inline JsValuePtr NewValue(const char* val)
     {
       return NewValue(std::string(val));
     }
     inline JsValuePtr NewValue(int val)
     {
       return NewValue(static_cast<int64_t>(val));
     }
     JsValuePtr NewObject();
     JsValuePtr NewCallback(v8::InvocationCallback callback);
-    static JsEngine& FromArguments(const v8::Arguments& arguments);
+    static JsEnginePtr FromArguments(const v8::Arguments& arguments);
     JsValueList ConvertArguments(const v8::Arguments& arguments);
 
     FileSystemPtr GetFileSystem();
     void SetFileSystem(FileSystemPtr val);
     WebRequestPtr GetWebRequest();
     void SetWebRequest(WebRequestPtr val);
     ErrorCallbackPtr GetErrorCallback();
     void SetErrorCallback(ErrorCallbackPtr val);
 
     class Context
     {
     public:
-      Context(const JsEngine& jsEngine);
+      Context(const JsEnginePtr jsEngine);
       virtual inline ~Context() {};
 
     private:
       const v8::Locker locker;
       const v8::HandleScope handleScope;
       const v8::Context::Scope contextScope;
     };
 
   private:
+    JsEngine();
+
     FileSystemPtr fileSystem;
     WebRequestPtr webRequest;
     ErrorCallbackPtr errorCallback;
     v8::Isolate* isolate;
     v8::Persistent<v8::Context> context;
   };
 }
 
 #endif