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 b4fc16941ed2017f500e7c63f524157cbeca72b6..63f9317e5004a6fb4ae5144c13628b09b19f058a 100644
--- a/components/mus/mus_app.cc
+++ b/components/mus/mus_app.cc
@@ -174,6 +174,11 @@ void MusApp::Initialize(shell::Connector* connector,
   event_source_ = ui::PlatformEventSource::CreateDefault();
 #endif
 
+  // This needs to happen after DeviceDataManager has been constructed. That
+  // happens either during OzonePlatform or PlatformEventSource initialization,
+  // so keep this line below both of those.
+  input_device_server_.RegisterAsObserver();
+
   // TODO(rjkroege): It is possible that we might want to generalize the
   // GpuState object.
   platform_display_init_params_.gpu_state = new GpuState();
@@ -194,6 +199,9 @@ bool MusApp::AcceptConnection(Connection* connection) {
   connection->AddInterface<mojom::WindowTreeFactory>(this);
   if (test_config_)
     connection->AddInterface<WindowServerTest>(this);
+
+  input_device_server_.RegisterInterface(connection);
+
   return true;
 }