Add module suffix in .mojom files for components/arc

components/arc/common/audio.mojom

 // 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 arc;
+module arc.mojom;
 
 // Use same switch values as kernel switch events.
 [Extensible]
 enum AudioSwitch {
   SW_HEADPHONE_INSERT = 0x02,
   SW_MICROPHONE_INSERT = 0x04
 };
 
 interface AudioInstance {
   // Notify plug states of headphone, microphone, etc.  Each switch state is
   // represented by the corresponding bit, if the bit is set then the switch
   // is plugged/inserted.
   NotifySwitchState(uint32 state);
 };