mus: Introduce AcceleratorRegistrar and AcceleratorHandler.

components/mus/public/interfaces/accelerator_registrar.mojom

+// Copyright 2015 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 "components/mus/public/interfaces/input_event_matcher.mojom";
+import "components/mus/public/interfaces/input_events.mojom";
+
+interface AcceleratorHandler {
+  OnAccelerator(uint32 id, Event event);
+};
+
+interface AcceleratorRegistrar {
+  AddAccelerator(uint32 id, EventMatcher matcher, AcceleratorHandler handler)
+      => (bool success);
+  RemoveAccelerator(uint32 id);
+};