Stop demo mode detection correctly.

Stop demo mode detection correctly.

|oobe_timer_| kept running after StopDetection() call. So in fact demo mode
detection remained active.

BUG=439956
TEST=Run 'chromeos=1' debug build with options --derelict-detection-timeout=10 --derelict-idle-timeout=10 --oobe-timer-interval=10. Enroll into enterprise domain, wait for 10 seconds at "Your device has successfully been enrolled." screen. Nothing should happen.

Committed: https://crrev.com/8ac4d6f3f2dd65f4a06d5bcd6c4976d0bb0bb1de
Cr-Commit-Position: refs/heads/master@{#309418}

[dzhioev (left Google), 2014-12-22 11:27:58]

dzhioev@chromium.org changed reviewers:
+ merkulova@chromium.org

[merkulova, 2014-12-22 11:42:18]

lgtm

[dzhioev (left Google), 2014-12-22 12:44:56]

The CQ bit was checked by dzhioev@chromium.org

[commit-bot: I haz the power, 2014-12-22 12:46:02]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/821013002/1

[commit-bot: I haz the power, 2014-12-22 13:44:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2014-12-22 13:44:42]

Patchset 1 (id:??) landed as
https://crrev.com/8ac4d6f3f2dd65f4a06d5bcd6c4976d0bb0bb1de
Cr-Commit-Position: refs/heads/master@{#309418}