Add Mojo IPC based input-device service.

components/mus/mus_app.cc

Index: components/mus/mus_app.cc
diff --git a/components/mus/mus_app.cc b/components/mus/mus_app.cc
index 52525daea891078d7201a537a87d1258d1fcbec4..93d946f5ecb0fe3dd18b2cbd2b1331f196b84a1b 100644
--- a/components/mus/mus_app.cc
+++ b/components/mus/mus_app.cc
@@ -156,6 +156,8 @@ void MusApp::Initialize(shell::Connector* connector,
   // in MUS, |InitializeForUI| will load the GL libraries.
   ui::OzonePlatform::InitializeForUI();
 
+  input_device_server_.RegisterAsObserver();
+
   // TODO(kylechar): We might not always want a US keyboard layout.
   ui::KeyboardLayoutEngineManager::GetKeyboardLayoutEngine()
       ->SetCurrentLayoutByName("us");
@@ -192,6 +194,9 @@ bool MusApp::AcceptConnection(Connection* connection) {
   connection->AddInterface<mojom::WindowTreeFactory>(this);
   if (test_config_)
     connection->AddInterface<WindowServerTest>(this);
+
+  input_device_server_.RegisterInterface(connection);
+
   return true;
 }