services/ui: Have an explicit lifetime/ownership of ui::GpuService.

ash/mus/window_manager_application.h

Index: ash/mus/window_manager_application.h
diff --git a/ash/mus/window_manager_application.h b/ash/mus/window_manager_application.h
index d2f4d27bb22e4f3cc461fd2ad55c80fc1b4e573c..15b6d8858a013e02690112fa88e0a5d102a5744d 100644
--- a/ash/mus/window_manager_application.h
+++ b/ash/mus/window_manager_application.h
@@ -28,6 +28,7 @@ class AuraInit;
 
 namespace ui {
 class Event;
+class GpuService;
 class WindowTreeClient;
 }
 
@@ -108,6 +109,7 @@ class WindowManagerApplication
   std::vector<mojo::InterfaceRequest<mojom::UserWindowController>>
       user_window_controller_requests_;
 
+  std::unique_ptr<ui::GpuService> gpu_service_;
   std::unique_ptr<WindowManager> window_manager_;
 
   std::set<AcceleratorRegistrarImpl*> accelerator_registrars_;