Add command to initiate garbage collection

include/AdblockPlus/JsEngine.h

 #ifndef ADBLOCKPLUS_JS_ENGINE_H
 #define ADBLOCKPLUS_JS_ENGINE_H
 
 #include <stdexcept>
 #include <string>
 #include <v8.h>
 
 class ErrorCallback;
 class FileReader;
 
 namespace AdblockPlus
 {
   class JsError : public std::runtime_error
   {
   public:
     JsError(const v8::Handle<v8::Value> exception);
   };
 
   class JsEngine
   {
   public:
     JsEngine(const FileReader* const fileReader,
              ErrorCallback* const errorCallback);
     void Evaluate(const std::string& source);
     void Load(const std::string& scriptPath);
     std::string Call(const std::string& functionName);
+    void Gc();
 
   private:
     const FileReader* const fileReader;
     v8::Persistent<v8::Context> context;
   };
 }
 
 #endif