Call GetSSLConfig on the IO thread.

Call GetSSLConfig on the IO thread.

SSLConfigService::GetSSLConfig is not thread-safe. This should also resolve the
test flakiness; the policy change applies on a thread hop, so the value must be
queried on a subsequently scheduled hop.

Add a DCHECK to SSLConfigServicePref to catch this in future.

BUG=496872
Committed: https://crrev.com/c360eb414c97fbcd2cb9025f77cb77e02b2fd7f3
Cr-Commit-Position: refs/heads/master@{#333088}

[davidben, 2015-06-04 22:39:41]

davidben@chromium.org changed reviewers:
+ agl@chromium.org, mnissler@chromium.org

[davidben, 2015-06-04 22:39:41]

I'm somewhat expecting the try bots to explode from other tests violating the
DCHECK, but we'll see.

[agl, 2015-06-04 22:53:00]

LGTM, thanks!

[Mattias Nissler (ping if slow), 2015-06-05 07:55:40]

LGTM

[davidben, 2015-06-05 16:15:31]

The CQ bit was checked by davidben@chromium.org

[davidben, 2015-06-05 16:15:31]

The patchset sent to the CQ was uploaded after l-g-t-m from agl@chromium.org,
mnissler@chromium.org
Link to the patchset: https://codereview.chromium.org/1164063004/#ps40001
(title: "enable the test")

[commit-bot: I haz the power, 2015-06-05 16:16:44]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1164063004/40001

[commit-bot: I haz the power, 2015-06-05 17:52:05]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-06-05 18:03:41]

Patchset 3 (id:??) landed as
https://crrev.com/c360eb414c97fbcd2cb9025f77cb77e02b2fd7f3
Cr-Commit-Position: refs/heads/master@{#333088}