[Cronet] Add support for Proxy Auto Config (PAC) script

[Cronet] Add support for Proxy Auto Config (PAC) script

Android system has a local http proxy server to evaluate
PAC scripts. Since Cronet does not depend on V8 for PAC
scripts, this CL changes so that we use this http proxy
server address and port instead of PAC script URLs. This CL
follows the approach that Android WebView used in
crrev.com/742023003.

BUG=527646
Committed: https://crrev.com/93a7ff793a87269f7556cc8c3541219e984c5073
Cr-Commit-Position: refs/heads/master@{#350029}

[xunjieli, 2015-09-04 18:20:53]

xunjieli@chromium.org changed reviewers:
+ pauljensen@chromium.org

[xunjieli, 2015-09-04 18:20:54]

Hi Paul, PTAL, but take your time. Unfortunately, we don't have a way to write a
test for this, so I tested the change locally.

[pauljensen, 2015-09-09 14:53:10]

lgtm

[pauljensen, 2015-09-09 14:54:41]

BTW I think this will conflict with https://codereview.chromium.org/1290243007/

[xunjieli, 2015-09-10 15:15:11]

On 2015/09/09 14:54:41, pauljensen wrote:
> BTW I think this will conflict with
https://codereview.chromium.org/1290243007/

Thanks for the heads up! Looks like the other one is about to land. I will wait
and rebase on that.

[xunjieli, 2015-09-21 21:17:22]

The CQ bit was checked by xunjieli@chromium.org

[xunjieli, 2015-09-21 21:17:23]

The patchset sent to the CQ was uploaded after l-g-t-m from
pauljensen@chromium.org
Link to the patchset: https://codereview.chromium.org/1318573006/#ps60001
(title: "Rebased")

[commit-bot: I haz the power, 2015-09-21 21:19:55]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1318573006/60001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1318573006/60001

[commit-bot: I haz the power, 2015-09-21 21:42:06]

Committed patchset #4 (id:60001)

[commit-bot: I haz the power, 2015-09-21 21:42:57]

Patchset 4 (id:??) landed as
https://crrev.com/93a7ff793a87269f7556cc8c3541219e984c5073
Cr-Commit-Position: refs/heads/master@{#350029}

[fujunweitongx, 2016-02-19 02:07:22]

> We should follow WebView's example https://codereview.chromium.org/742023003/,
to set up support for PAC in Cronet.
How to set up PAC?