Made sure FilterEngine instances are always initialized

src/JsEngine.cpp

Index: src/JsEngine.cpp
===================================================================
--- a/src/JsEngine.cpp
+++ b/src/JsEngine.cpp
@@ -88,16 +88,34 @@ AdblockPlus::JsValuePtr AdblockPlus::JsE
   const v8::TryCatch tryCatch;
   const v8::Handle<v8::Script> script = CompileScript(source, filename);
   CheckTryCatch(tryCatch);
   v8::Local<v8::Value> result = script->Run();
   CheckTryCatch(tryCatch);
   return JsValuePtr(new JsValue(shared_from_this(), result));
 }
 
+void AdblockPlus::JsEngine::SetEventCallback(const std::string& eventName,
+    AdblockPlus::JsEngine::EventCallback callback)
+{
+  eventCallbacks[eventName] = callback;
+}
+
+void AdblockPlus::JsEngine::RemoveEventCallback(const std::string& eventName)
+{
+  eventCallbacks.erase(eventName);
+}
+
+void AdblockPlus::JsEngine::TriggerEvent(const std::string& eventName)
+{
+  EventMap::iterator it = eventCallbacks.find(eventName);
+  if (it != eventCallbacks.end())
+    it->second();
+}
+
 void AdblockPlus::JsEngine::Gc()
 {
   while (!v8::V8::IdleNotification());
 }
 
 AdblockPlus::JsValuePtr AdblockPlus::JsEngine::NewValue(const std::string& val)
 {
   const Context context(shared_from_this());