V2 app support step2 : Use NativeAppWindow for Activity's window.

athena/activity/activity_view_manager_impl.cc

Index: athena/activity/activity_view_manager_impl.cc
diff --git a/athena/activity/activity_view_manager_impl.cc b/athena/activity/activity_view_manager_impl.cc
index 76d40d497328a51acfeff6036c600279dc94536c..240e5bd2ba1093615af30737b60852f6772086ed 100644
--- a/athena/activity/activity_view_manager_impl.cc
+++ b/athena/activity/activity_view_manager_impl.cc
@@ -24,10 +24,12 @@ typedef std::map<Activity*, views::Widget*> ActivityWidgetMap;
 
 views::Widget* CreateWidget(Activity* activity) {
   ActivityViewModel* view_model = activity->GetActivityViewModel();
-  views::Widget* widget = new views::Widget;
+  views::Widget* widget = view_model->CreateWidget();
+  if (widget)
+    return widget;
+  widget = new views::Widget;
   views::Widget::InitParams params(views::Widget::InitParams::TYPE_WINDOW);
   params.delegate = new ActivityWidgetDelegate(view_model);
-  params.activatable = views::Widget::InitParams::ACTIVATABLE_YES;
   widget->Init(params);
   return widget;
 }