Refactors DockedWindowLayoutManager in terms of ash/wm/common

ash/system/user/tray_user.h

Index: ash/system/user/tray_user.h
diff --git a/ash/system/user/tray_user.h b/ash/system/user/tray_user.h
index 3f93025d50e23cd06bc86cc767e7d00d04c41135..39447c1bf3fb6e046453d133112b613cb52ae2d7 100644
--- a/ash/system/user/tray_user.h
+++ b/ash/system/user/tray_user.h
@@ -69,7 +69,7 @@ class ASH_EXPORT TrayUser : public SystemTrayItem,
   void DestroyTrayView() override;
   void DestroyDefaultView() override;
   void UpdateAfterLoginStatusChange(user::LoginStatus status) override;
-  void UpdateAfterShelfAlignmentChange(ShelfAlignment alignment) override;
+  void UpdateAfterShelfAlignmentChange(wm::ShelfAlignment alignment) override;
 
   // Overridden from UserObserver.
   void OnUserUpdate() override;