Move demo mode preference registration.

Move demo mode preference registration.
Move the register preferences code for the demo mode detector to the correct location.

Need owners reviews for c/b/prefs and c/b/ui/webui/login.

R=merkulova@chromium.org, mnissler@chromium.org, nkostylev@chromium.org
BUG=None.

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=283420

[Nikita (slow), 2014-07-14 09:26:57]

lgtm

[rkc, 2014-07-14 10:29:43]

The CQ bit was checked by rkc@chromium.org

[commit-bot: I haz the power, 2014-07-14 10:30:49]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/rkc@chromium.org/381833002/1

[commit-bot: I haz the power, 2014-07-14 12:12:50]

FYI, CQ is re-trying this CL (attempt #1).
The failing builders are:
  chromium_presubmit on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/chromium_presubmit/bu...)
  mac_chromium_rel on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/mac_chromium_rel/buil...)

[commit-bot: I haz the power, 2014-07-14 12:16:24]

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

[commit-bot: I haz the power, 2014-07-14 12:16:25]

Try jobs failed on following builders:
  chromium_presubmit on tryserver.chromium
(http://build.chromium.org/p/tryserver.chromium/builders/chromium_presubmit/bu...)

[merkulova, 2014-07-16 10:38:12]

lgtm

[rkc, 2014-07-16 11:05:21]

Adding battre@ for c/b/prefs owners review since Mattias is OOO.

[battre, 2014-07-16 11:19:55]

lgtm

[rkc, 2014-07-16 17:43:49]

The CQ bit was checked by rkc@chromium.org

[commit-bot: I haz the power, 2014-07-16 17:46:02]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/rkc@chromium.org/381833002/1

[commit-bot: I haz the power, 2014-07-16 17:54:06]

Change committed as 283420