Add always on top windows to the alt+tab list

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index ef6557a6ed77ce77f83a0a7b65151c08f9208493..cfd7b502d74a0e6992e118f6f6dbc95aa97310d9 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -697,6 +697,7 @@ void Shell::InitRootWindowController(
   DCHECK(visibility_controller_.get());
   DCHECK(drag_drop_controller_.get());
   DCHECK(capture_controller_.get());
+  DCHECK(window_cycle_controller_.get());
 
   root_window->set_focus_manager(focus_manager_.get());
   input_method_filter_->SetInputMethodPropertyInRootWindow(root_window);
@@ -728,6 +729,8 @@ void Shell::InitRootWindowController(
       root_window->GetChildById(internal::kShellWindowId_AlwaysOnTopContainer));
   root_window->SetProperty(internal::kAlwaysOnTopControllerKey,
                            always_on_top_controller);
+
+  window_cycle_controller_->OnRootWindowAdded(root_window);
 }
 
 ////////////////////////////////////////////////////////////////////////////////