Enable ash window cycle UI by default.

ui/app_list/presenter/app_list_presenter_impl.cc

Index: ui/app_list/presenter/app_list_presenter_impl.cc
diff --git a/ui/app_list/presenter/app_list_presenter_impl.cc b/ui/app_list/presenter/app_list_presenter_impl.cc
index 572528b3a3eb6e808afac5c9fc400922067f9a98..cd181d1657ed606e57ce605f0824b4b262a8eb1d 100644
--- a/ui/app_list/presenter/app_list_presenter_impl.cc
+++ b/ui/app_list/presenter/app_list_presenter_impl.cc
@@ -80,12 +80,14 @@ void AppListPresenterImpl::Dismiss() {
 
   is_visible_ = false;
 
-  // Our widget is currently active. When the animation completes we'll hide
-  // the widget, changing activation. If a menu is shown before the animation
-  // completes then the activation change triggers the menu to close. By
-  // deactivating now we ensure there is no activation change when the
-  // animation completes and any menus stay open.
-  view_->GetWidget()->Deactivate();
+  // The dismissal may have occurred in response to the app list losing
+  // activation. Otherwise, our widget is currently active. When the animation
+  // completes we'll hide the widget, changing activation. If a menu is shown
+  // before the animation completes then the activation change triggers the menu
+  // to close. By deactivating now we ensure there is no activation change when
+  // the animation completes and any menus stay open.
+  if (view_->GetWidget()->IsActive())

[Evan Stade, 2016/08/12 22:51:58]

This is necessary because otherwise Alt+Tabbing while the app list is up causes
the app list to deactivate and pass activation to some other random window,
stealing activation from the window cycle ui.

I've added test coverage for this in
WindowCycleControllerTest.SelectingHidesAppList

+    view_->GetWidget()->Deactivate();
 
   presenter_delegate_->OnDismissed();
   ScheduleAnimation();