mash: Add status area container to mash window manager

mash/wm/window_manager_application.h

Index: mash/wm/window_manager_application.h
diff --git a/mash/wm/window_manager_application.h b/mash/wm/window_manager_application.h
index 7741e5197bab0b31b07eb1edf418abde4d882870..867e8be974b70838cccfd2766540a308653cc327 100644
--- a/mash/wm/window_manager_application.h
+++ b/mash/wm/window_manager_application.h
@@ -40,6 +40,7 @@ namespace wm {
 class AcceleratorRegistrarImpl;
 class RootWindowController;
 class RootWindowsObserver;
+class ShelfLayoutImpl;
 class UserWindowControllerImpl;
 
 class WindowManagerApplication
@@ -115,8 +116,9 @@ class WindowManagerApplication
   std::unique_ptr<views::ScreenMus> screen_;
   std::unique_ptr<views::AuraInit> aura_init_;
 
-  // The ShelfLayout object is created once OnEmbed() is called. Until that
+  // The |shelf_layout_| object is created once OnEmbed() is called. Until that
   // time |shelf_layout_requests_| stores pending interface requests.
+  std::unique_ptr<ShelfLayoutImpl> shelf_layout_;
   mojo::BindingSet<mojom::ShelfLayout> shelf_layout_bindings_;
   std::vector<std::unique_ptr<mojo::InterfaceRequest<mojom::ShelfLayout>>>
       shelf_layout_requests_;