Add Mojo IPC based input-device service.

components/mus/public/interfaces/input_devices/input_device_server.mojom

Index: components/mus/public/interfaces/input_devices/input_device_server.mojom
diff --git a/components/mus/public/interfaces/input_devices/input_device_server.mojom b/components/mus/public/interfaces/input_devices/input_device_server.mojom
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+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+module mus.mojom;
+
+import "ui/events/devices/mojo/input_devices.mojom";
+
+// Receives updates about changes to input-devices. See InputDeviceServer for
+// the expected behaviour.
+interface InputDeviceObserverMojo {
+  // Is called when the list of keyboards changes.
+  OnKeyboardDeviceConfigurationChanged(array<ui.mojom.InputDevice> devices);
+
+  // Is called when the list of touchscreens changes.
+  OnTouchscreenDeviceConfigurationChanged(
+      array<ui.mojom.TouchscreenDevice> devices);
+
+  // Is called when the list of mice changes.
+  OnMouseDeviceConfigurationChanged(array<ui.mojom.InputDevice> devices);
+
+  // Is called when the list of touchpads changes.
+  OnTouchpadDeviceConfigurationChanged(array<ui.mojom.InputDevice> devices);
+
+  // Is called once all of the input-device lists are available. This will
+  // always be the first call that an observer receives.
+  OnDeviceListsComplete(
+      array<ui.mojom.InputDevice> keyboard_devices,
+      array<ui.mojom.TouchscreenDevice> touchscreen_devices,
+      array<ui.mojom.InputDevice> mouse_devices,
+      array<ui.mojom.InputDevice> touchpad_devices);
+};
+
+// Sends updates about input-devices to observers.
+interface InputDeviceServer {
+  // Adds an InputDeviceObserverMojo in another process as an observer to get
+  // notified of changes to input-devices over Mojo IPC. If all input-device
+  // lists are complete when a new observer connects, the implementation will
+  // immediately call OnDeviceListsComplete() with the input-device lists. If
+  // not, the implementation will wait until all input-device lists are complete
+  // then call OnDeviceListsComplete() for all connected observers.
+  AddObserver(InputDeviceObserverMojo observer);
+};