Use SequencedTaskRunner rather than SingledThreadedTaskRunner for passing io_task_runner

Use SequencedTaskRunner rather than SingledThreadedTaskRunner for passing io_task_runner to ProxyConfigService.

In practice the io_task_runner will be a SingleThreadedTaskRunner, but this thread affinity doesn't need to be a contractual guarantee for ProxyConfigService implementations.

BUG=735368
Review-Url: https://codereview.chromium.org/2957433002
Cr-Commit-Position: refs/heads/master@{#481955}
Committed: https://chromium.googlesource.com/chromium/src/+/98e76eb9375e2db29291163aeec9f0bdf9ff85cb

[eroman, 2017-06-22 20:42:19]

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

[commit-bot: I haz the power, 2017-06-22 20:42:53]

Dry run: CQ is trying da patch.

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

[eroman, 2017-06-22 20:47:20]

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

[commit-bot: I haz the power, 2017-06-22 20:47:25]

Dry run: CQ is trying da patch.

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

[commit-bot: I haz the power, 2017-06-22 21:05:49]

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

[commit-bot: I haz the power, 2017-06-22 21:05:50]

Dry run: Try jobs failed on following builders:
  cast_shell_linux on master.tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/cast_shell_linu...)

[eroman, 2017-06-22 22:33:33]

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

[commit-bot: I haz the power, 2017-06-22 22:34:13]

Dry run: CQ is trying da patch.

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

[eroman, 2017-06-22 22:35:52]

Description was changed from

==========
Use SequencedTaskRunner in place of SingleThreadTaskRunner throughout
ProxyConfigService.

SingleThreadTaskRunner was being used for two things:

  (1) Passing around the IO thread -- SequencedTaskRunner is fine as we
      don't need to contractually guarantee thread affinity to
      ProxyConfigService implementations. But in practice it will be as
      it is the IO thread.

  (2) Passing the glib thread to ProxyConfigServiceLinux. OK, I admit
      this is slightly questionable... The consuming code in
      ProxyConfigServiceLinux doesn't rely on thread affinity beyond
      the fact that glib can safely be operated from this thread (which
      is already an attribute reflected by its name). In practice
      use of glib implies thread affinity so the two annotations are
      redundant.

BUG=735368
==========

to

==========
Use SequencedTaskRunner rather than SingledThreadedTaskRunner for passing
io_task_runner to ProxyConfigService.

In practice the io_task_runner will be a SingleThreadedTaskRunner, but this
thread affinity doesn't need to be a contractual guarantee for
ProxyConfigService implementations.

BUG=735368
==========

[commit-bot: I haz the power, 2017-06-23 01:10:37]

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

[commit-bot: I haz the power, 2017-06-23 01:10:38]

Dry run: This issue passed the CQ dry run.

[eroman, 2017-06-23 01:44:40]

eroman@chromium.org changed reviewers:
+ mmenke@chromium.org

[mmenke, 2017-06-23 15:20:45]

LGTM!

[eroman, 2017-06-23 18:01:05]

The CQ bit was checked by eroman@chromium.org

[commit-bot: I haz the power, 2017-06-23 18:01:20]

CQ is trying da patch.

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

[commit-bot: I haz the power, 2017-06-23 18:07:04]

CQ is committing da patch.

Bot data: {"patchset_id": 40001, "attempt_start_ts": 1498240865685640,
"parent_rev": "3abd33dfed74c46e375b24c7a1e540e549de3bda", "commit_rev":
"98e76eb9375e2db29291163aeec9f0bdf9ff85cb"}

[commit-bot: I haz the power, 2017-06-23 18:07:18]

Description was changed from

==========
Use SequencedTaskRunner rather than SingledThreadedTaskRunner for passing
io_task_runner to ProxyConfigService.

In practice the io_task_runner will be a SingleThreadedTaskRunner, but this
thread affinity doesn't need to be a contractual guarantee for
ProxyConfigService implementations.

BUG=735368
==========

to

==========
Use SequencedTaskRunner rather than SingledThreadedTaskRunner for passing
io_task_runner to ProxyConfigService.

In practice the io_task_runner will be a SingleThreadedTaskRunner, but this
thread affinity doesn't need to be a contractual guarantee for
ProxyConfigService implementations.

BUG=735368

Review-Url: https://codereview.chromium.org/2957433002
Cr-Commit-Position: refs/heads/master@{#481955}
Committed:
https://chromium.googlesource.com/chromium/src/+/98e76eb9375e2db29291163aeec9...
==========

[commit-bot: I haz the power, 2017-06-23 18:07:19]

Committed patchset #3 (id:40001) as
https://chromium.googlesource.com/chromium/src/+/98e76eb9375e2db29291163aeec9...