Adding ArcBridge Interface for Volume Update Requests

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.
 
-// Next MinVersion: 3
+// Next MinVersion: 4
 
 module arc.mojom;
 
 // Use same switch values as kernel switch events.
 [Extensible]
 enum AudioSwitch {
   SW_HEADPHONE_INSERT = 0x02,
   SW_MICROPHONE_INSERT = 0x04
 };
 
+// Next method ID:2
 interface AudioHost {
   // Tells the host to show the volume controls.
   ShowVolumeControls@0();
+
+  // Request that the volume be changed to |volume|
+  // |volume| is of the range [0, 100]
+  [MinVersion=3] OnVolumeUpdateRequest@1(float volume);

[Luis Héctor Chávez, 2017/04/13 14:21:25]

nit: OnSystemVolumeUpdateRequest

Also mention that this is a privileged API and should only be used on
whitelisted cases.

[dcheng, 2017/04/13 18:02:40]

Can you clarify what that means? We have no way of enforcing that from the
browser process, right? So really anyone can call it.

[Luis Héctor Chávez, 2017/04/13 18:05:40]

Yes, we're trusting that the other side will only call this in appropriate
occasions. Otherwise random apps will be able to modify the system volume and
we'd like to avoid that. The best we can do here is document the intended usage.

[yueli, 2017/06/02 19:10:13]

Done.

 };
 
 // Next method ID: 3
 interface AudioInstance {
   // Establishes full-duplex communication with the host.
   [MinVersion=1] Init@1(AudioHost host);
 
   // 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@0(uint32 state);
 
   // Notify volume and mute state.
   // volume ranges from 0 to 100.
   // muted == true if audio is muted.
   [MinVersion=2] NotifyVolumeState@2(uint32 volume, bool muted);
 };