GpuArcVideoService

components/arc/common/video.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;
 
 interface VideoHost {
   // Notifies Chrome a request for ipc channel of video acceleration.

[Owen Lin, 2016/03/14 08:45:52]

... for an ipc channel ... ?

But why the name is OnXXX. Usually XXX will be some kind of event.

Can we just use requestArcVideoAcceleratorChannel?

The comment could be:
Requests an ipc channel from Chrome to be used in the video accelerator. Will
this call fail (due to resource limitation)? If yet, you should document what
happens.


In addition, why a pid is required here? Do we only allow one
ArcVideoAccelerator per process? Please also explain what's is a token? How is
it being used?

[kcwu, 2016/03/14 12:55:49]

The naming "On..." follows other arc interfaces (*.mojom in this folder). On*
for Host side and no "On" for Instance side.
Done.
They are required to establish mojo channel and create message pipes. 

There are two steps to create message pipe using the new mojo edk.
(It's no longer a simple unix pipe as before)
1. exchange a pipe handle for mojo internal use. ChildProcessLaunched(pid) and
SetParentPipeHandle(handle) are called on parent and child side, respectively.
2. exchange a (random) token to create pipe for mojo interfaces. Then
CreateParentMessagePipe(token) and CreateChildMessagePipe(token) are called on
parent and child side, respectively.

I added comments for them. However, I don't want to add too much since it is
kind of mojo low level things.

-  OnRequestArcVideoAcceleratorChannel() => (handle channel_handle);
+  OnRequestArcVideoAcceleratorChannel(uint32 pid) => (handle channel_handle,
+                                                      string token);
 };
 
 interface VideoInstance {
   // Establishes full-duplex communication with the host.
   Init(VideoHost host_ptr);
 };