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 {

[Ben Goodger (Google), 2015/12/01 03:47:32]

While it's clever to control the lifetime of namespaces by the lifetime of this
object, and bind the lifetime of this object to the lifetime of the pipe, it
feels a bit heavyweight that a client has to keep this pipe open effectively
forever. I wonder if there's a way to have a single registry and scope the
lifetime of the entries to the AcceleratorHandler pipe which must remain open
for obvious reasons?

[sadrul, 2015/12/01 15:17:24]

I have changed this so that (1) the lifetime of the namespace is tied with the
lifetime of the AcceleratorRegistrar, i.e. different clients still have
different namespace. I think we still need this to avoid accelerator id
conflicts from different clients. (2) the accelerators are removed when the
associated AcceleratorHandler is destroyed. So the client no longer needs to
keep the AcceleratorRegistrar alive, and can destroy it as soon as all the
accelerators are installed. The accelerators will work correctly as long as the
AcceleratorHandlers are kept alive.

I have updated the CL description accordingly.

+  AddAccelerator(uint32 id, EventMatcher matcher, AcceleratorHandler handler)
+      => (bool success);
+  RemoveAccelerator(uint32 id);
+};