[Chromoting] Use ProcessStatsSender in host process

[Chromoting] Use ProcessStatsSender in host process

This is part of the change in host side to send process resourece usage
information to the client. It contains,
1. Start a new channel (proc_stats) to dedicate sending process resource usage.
  The change is mainly in ProcessStatsDispatcher class.
2. ConnectionToClient::stats_stub().
  Returns a ProcessStatsStub to deliver the information.
  WebRtcConnectionToClient uses ProcessStatsDispatcher, other implementations
  returns nullptr or FakeProcessStatsDispatcher.
3. ClientSession starts ProcessStatsSender in OnConnectionAuthenticated() and
stops it in OnConnectionClosed().

A coming change will forward the process usage from Desktop Process to Network
Process.

BUG=650926

[Hzj_jie, 2017-05-03 00:09:17]

The CQ bit was checked by zijiehe@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-05-03 00:09:47]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Hzj_jie, 2017-05-03 00:30:59]

The CQ bit was checked by zijiehe@chromium.org to run a CQ dry run

[Hzj_jie, 2017-05-03 00:31:14]

Patchset #1 (id:1) has been deleted

[commit-bot: I haz the power, 2017-05-03 00:31:20]

Dry run: CQ is trying da patch.

Follow status at:
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[Hzj_jie, 2017-05-03 00:32:24]

Description was changed from

==========
[Chromoting] Use ProcessStatsSender in host process

BUG=650926
==========

to

==========
[Chromoting] Use ProcessStatsSender in host process

This is part of the change in host side to send process resourece usage
information to the client. It contains,
1. Start a new channel (proc_stats) to dedicate sending process resource usage.
  The change is mainly in ProcessStatsDispatcher class.
2. ConnectionToClient::stats_stub().
  Returns a ProcessStatsStub to deliver the information.
  WebRtcConnectionToClient uses ProcessStatsDispatcher, other implementations
  returns nullptr or FakeProcessStatsDispatcher.
3. ClientSession starts ProcessStatsSender in OnConnectionAuthenticated() and
stops it in OnConnectionClosed().

A coming change will forward the process usage from Desktop Process to Network
Process.

BUG=650926
==========

[commit-bot: I haz the power, 2017-05-03 02:11:54]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2017-05-03 02:11:55]

Dry run: This issue passed the CQ dry run.

[Hzj_jie, 2017-05-03 06:07:41]

zijiehe@chromium.org changed reviewers:
+ jamiewalch@chromium.org, joedow@chromium.org

[Hzj_jie, 2017-05-03 18:57:45]

zijiehe@chromium.org changed reviewers:
- jamiewalch@chromium.org, joedow@chromium.org