Change |use_alternative_service| not to disable Alternate Protocols.

Change |use_alternative_service| not to disable Alternate Protocols.

Currently, HttpNetworkSession::Params::use_alternative_service controls both
Alternate Protocols and Alternative Services.  However, Alternate Protocols is
fully rolled out, therefore there is not need to disable it.

This CL changes |use_alternative_service| to
 * disable parsing Alt-Svc headers (but not Alternate-Protocol ones);
 * disable following saved alternative service entries that point to different
   hosts (but not ones that point to the same host).
The latter is necessary because a browser session might have this flag enabled
and might save alternative services to disk, which we do not really want to
follow in the next browser session if the flag is disabled.  (Ones discovered
through Alt-Svc pointing to the same host will still be respected.)

BUG=524141
Committed: https://crrev.com/54ec34b7c174848672fc3ea08aba7289630df4a3
Cr-Commit-Position: refs/heads/master@{#345640}

[Bence, 2015-08-21 14:23:00]

bnc@chromium.org changed reviewers:
+ rch@chromium.org

[Bence, 2015-08-21 14:23:00]

Ryan: PTAL.  Thanks.

[Ryan Hamilton, 2015-08-24 18:18:29]

This change looks great. Needs tests, though.

[Bence, 2015-08-26 17:19:28]

PTAL.

On 2015/08/24 18:18:29, Ryan Hamilton wrote:
> This change looks great. Needs tests, though.

Voilà les tests.  Sorry for the oversight.

[Ryan Hamilton, 2015-08-26 18:38:45]

Thanks! LGTM

[Bence, 2015-08-26 18:39:42]

The CQ bit was checked by bnc@chromium.org

[commit-bot: I haz the power, 2015-08-26 18:40:03]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1310583002/40001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1310583002/40001

[commit-bot: I haz the power, 2015-08-26 19:35:04]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-08-26 19:35:58]

Patchset 3 (id:??) landed as
https://crrev.com/54ec34b7c174848672fc3ea08aba7289630df4a3
Cr-Commit-Position: refs/heads/master@{#345640}