arc-bridge: Move most methods to Mojo interfaces

components/arc/common/input.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 arc;
+
+interface InputInstance {
+  // Registers a virtual input device on the container side.
+  // |name| is the device name, like "Chrome OS Keyboard".
+  // |device_type| is the device type, like "keyboard".
+  // The virtual device will be reading 'struct input_event's from |fd|.  The
+  // ownership of |fd| will be transferred to the receiver, so the sender must
+  // not close it.
+  RegisterInputDevice(string name,
+                      string device_type,
+                      handle fd);
+};