AppListController now responsible for ensuring app list stays centered.

ash/wm/app_list_controller.h

Index: ash/wm/app_list_controller.h
diff --git a/ash/wm/app_list_controller.h b/ash/wm/app_list_controller.h
index c2eb0ad3589168891b6d802fae394af6eea0bfa3..b8c212bfcfca125250ba3326c0e44927e239ef13 100644
--- a/ash/wm/app_list_controller.h
+++ b/ash/wm/app_list_controller.h
@@ -125,6 +125,9 @@ class AppListController : public ui::EventHandler,
   // Whether we should show or hide app list widget.
   bool is_visible_;
 
+  // Whether the app list should remain centered.
+  bool is_centered_;
+
   // The AppListView this class manages, owned by its widget.
   app_list::AppListView* view_;