Enable InputDeviceServer/InputDeviceClient in mash.

components/mus/input_devices/input_device_server.h

Index: components/mus/input_devices/input_device_server.h
diff --git a/components/mus/input_devices/input_device_server.h b/components/mus/input_devices/input_device_server.h
index 0f98a6634779e3af8d534f855033f12a8649c53b..af0e0e704e6014bd533a8280504f91944ce86342 100644
--- a/components/mus/input_devices/input_device_server.h
+++ b/components/mus/input_devices/input_device_server.h
@@ -29,11 +29,13 @@ class InputDeviceServer
 
   // Registers this instance as a local observer with DeviceDataManager.
   void RegisterAsObserver();
+  bool IsRegisteredAsObserver() const;
 
-  // Registers interface with the shell connection so remote observers can
-  // connect. You should have already called RegisterAsObserver() to get
-  // local input-device event updates.
-  void RegisterInterface(shell::Connection* connection);
+  // Adds interface with the shell connection so remote observers can connect.
+  // You should have already called RegisterAsObserver() to get local
+  // input-device event updates and checked it was successful by calling
+  // IsRegisteredAsObserver().
+  void AddInterface(shell::Connection* connection);
 
   // mojom::InputDeviceServer:
   void AddObserver(mojom::InputDeviceObserverMojoPtr observer) override;