mash: Convert shelf to wm::WmWindow types, part 1

ash/system/status_area_widget.h

Index: ash/system/status_area_widget.h
diff --git a/ash/system/status_area_widget.h b/ash/system/status_area_widget.h
index d8459c7bede5ffc6fbc5028d4ca6746f2186a4f5..6b00f202fa8d861953e45128e11083fe1e9710b9 100644
--- a/ash/system/status_area_widget.h
+++ b/ash/system/status_area_widget.h
@@ -22,10 +22,13 @@ class WebNotificationTray;
 class LogoutButtonTray;
 class VirtualKeyboardTray;
 #endif
+namespace wm {
+class WmWindow;
+}
 
 class ASH_EXPORT StatusAreaWidget : public views::Widget {
  public:
-  StatusAreaWidget(aura::Window* status_container, ShelfWidget* shelf_widget);
+  StatusAreaWidget(wm::WmWindow* status_container, ShelfWidget* shelf_widget);
   ~StatusAreaWidget() override;
 
   // Creates the SystemTray, WebNotificationTray and LogoutButtonTray.