Don't do field trials if Instant is explicitly enabled.

Don't do field trials if Instant is explicitly enabled.

http://crrev.com/134073 removed the check for prefs::kInstantEnabledOnce for
some field trial modes. So it became possible for Instant to be explicitly
enabled, and yet for IsHiddenExperiment() to return true (which would cause
incorrect logic in InstantController::Update() and other places). Fix this by
checking that prefs::kInstantEnabled is not set.

BUG=none
TEST=none


Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=134486

[sreeram, 2012-04-27 19:11:46]

Please review.

[sky, 2012-04-27 20:34:31]

LGTM

[commit-bot: I haz the power, 2012-04-28 22:16:46]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sreeram@chromium.org/10254014/1

[commit-bot: I haz the power, 2012-04-28 22:23:52]

Try job failure for 10254014-1 on win_rel for step "update".
http://build.chromium.org/p/tryserver.chromium/buildstatus?builder=win_rel&nu...

Step "update" is always a major failure.
Look at the try server FAQ for more details.

[commit-bot: I haz the power, 2012-04-28 23:14:25]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/sreeram@chromium.org/10254014/1

[commit-bot: I haz the power, 2012-04-29 00:45:53]

Change committed as 134486