Refactors DockedWindowLayoutManager in terms of ash/wm/common

ash/system/user/tray_user_separator.h

Index: ash/system/user/tray_user_separator.h
diff --git a/ash/system/user/tray_user_separator.h b/ash/system/user/tray_user_separator.h
index 76fd9b281f6d5a3294c4159bd450600fe45a64e1..696e2c81bc11c34e0e97c7bfa15c9b4d80b08c98 100644
--- a/ash/system/user/tray_user_separator.h
+++ b/ash/system/user/tray_user_separator.h
@@ -31,7 +31,7 @@ class ASH_EXPORT TrayUserSeparator : public SystemTrayItem {
   void DestroyDefaultView() override;
   void DestroyDetailedView() override {}
   void UpdateAfterLoginStatusChange(user::LoginStatus status) override {}
-  void UpdateAfterShelfAlignmentChange(ShelfAlignment alignment) override {}
+  void UpdateAfterShelfAlignmentChange(wm::ShelfAlignment alignment) override {}
 
   // True if the separator gets shown.
   bool separator_shown_;