Add Mojo IPC based input-device service.

ash/mus/sysui_application.h

Index: ash/mus/sysui_application.h
diff --git a/ash/mus/sysui_application.h b/ash/mus/sysui_application.h
index 4e8afcee7dca69a0601bf8dbe6e88d3ec96e08dd..6eb35e7238cb5f98bc5a42590b7ccf98365eedb3 100644
--- a/ash/mus/sysui_application.h
+++ b/ash/mus/sysui_application.h
@@ -8,6 +8,7 @@
 #include <memory>
 
 #include "base/macros.h"
+#include "components/input_device_service/input_device_client.h"
 #include "mash/shelf/public/interfaces/shelf.mojom.h"
 #include "mojo/public/cpp/bindings/binding_set.h"
 #include "services/shell/public/cpp/shell_client.h"
@@ -43,6 +44,8 @@ class SysUIApplication
   mojo::BindingSet<mash::shelf::mojom::ShelfController>
       shelf_controller_bindings_;
 
+  input_device::InputDeviceClient input_device_client_;
+
   DISALLOW_COPY_AND_ASSIGN(SysUIApplication);
 };