Add missing call to parent method of GApplication::shutdown, implement...

Add missing call to parent method of GApplication::shutdown, implement GApplication::startup (#136836)

Fixes a warning introduced in https://github.com/flutter/flutter/pull/136780 and adds the other related function.

packages/flutter_tools/templates/app_shared/linux.tmpl/my_application.cc.tmpl

@@ -81,11 +81,22 @@ static gboolean my_application_local_command_line(GApplication* application, gch
   return TRUE;
 }
 
+// Implements GApplication::startup.
+static void my_application_startup(GApplication* application) {
+  //MyApplication* self = MY_APPLICATION(object);
+
+  // Perform any actions required at application startup.
+
+  G_APPLICATION_CLASS(my_application_parent_class)->startup(application);
+}
+
 // Implements GApplication::shutdown.
 static void my_application_shutdown(GApplication* application) {
   //MyApplication* self = MY_APPLICATION(object);
 
   // Perform any actions required at application shutdown.
+
+  G_APPLICATION_CLASS(my_application_parent_class)->shutdown(application);
 }
 
 // Implements GObject::dispose.
@@ -98,6 +109,7 @@ static void my_application_dispose(GObject* object) {
 static void my_application_class_init(MyApplicationClass* klass) {
   G_APPLICATION_CLASS(klass)->activate = my_application_activate;
   G_APPLICATION_CLASS(klass)->local_command_line = my_application_local_command_line;
+  G_APPLICATION_CLASS(klass)->startup = my_application_startup;
   G_APPLICATION_CLASS(klass)->shutdown = my_application_shutdown;
   G_OBJECT_CLASS(klass)->dispose = my_application_dispose;
 }