Shutdown the status tray before the system tray delegate.

ash/shell.h

Index: ash/shell.h
diff --git a/ash/shell.h b/ash/shell.h
index 8401a6c3c433006bad17444d02e03a82388d4396..c61aa031c91561b2a4bbace016eee78c9921ee67 100644
--- a/ash/shell.h
+++ b/ash/shell.h
@@ -605,6 +605,9 @@ class ASH_EXPORT Shell : public SystemModalContainerEventFilterDelegate,
   // Initializes the root window so that it can host browser windows.
   void InitRootWindow(aura::Window* root_window);
 
+  // Hides the shelf view if any are visible.
+  void HideShelf();
+
   // ash::SystemModalContainerEventFilterDelegate overrides:
   bool CanWindowReceiveEvents(aura::Window* window) override;