port plugin to package

example/windows/runner/flutter_window.cpp

@@ -31,6 +31,11 @@ bool FlutterWindow::OnCreate() {
     this->Show();
   });
 
+  // Flutter can complete the first frame before the "show window" callback is
+  // registered. The following call ensures a frame is pending to ensure the
+  // window is shown. It is a no-op if the first frame hasn't completed yet.
+  flutter_controller_->ForceRedraw();
+
   return true;
 }