Delay the unresponsive event shortly.

It could happen that a window became responsive immediately after the
unresponsive message is sent, like after showing a context menu
synchronously.

atom/browser/native_window.h

@@ -248,6 +248,12 @@ class NativeWindow : public brightray::DefaultWebContentsDelegate,
   gfx::Image icon_;
 
  private:
+  // Schedule a notification unresponsive event.
+  void ScheduleUnresponsiveEvent(int ms);
+
+  // Dispatch unresponsive event to observers.
+  void NotifyWindowUnresponsive();
+
   // Called when CapturePage has done.
   void OnCapturePageDone(const CapturePageCallback& callback,
                          bool succeed,