fix assertion in Logger::CurrentTimeEvent with --prof

fix assertion in Logger::CurrentTimeEvent with --prof

assertion did match the conditions under which this method gets called
(Runtime_DateCurrentTime). The bug got introduced as part of this change:
https://codereview.chromium.org/802333002

The assertion crash can be reproduced using:
% out/Debug/d8 --prof -e 'new Date();'

R=jkummerow@chromium.org
BUG=

Committed: https://crrev.com/1f03256de37aaa1b1cbe81d56122defa0ad9aa9a
Cr-Commit-Position: refs/heads/master@{#28096}

[Jakob Kummerow, 2015-04-28 08:30:58]

LGTM, thanks for the patch.

Note that using --prof in Debug mode can be very misleading, unless you're
specifically interested in Debug mode behavior.

[Jakob Kummerow, 2015-04-28 08:31:06]

The CQ bit was checked by jkummerow@chromium.org

[commit-bot: I haz the power, 2015-04-28 08:31:12]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1104303002/1

[commit-bot: I haz the power, 2015-04-28 08:54:21]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-28 08:54:33]

Patchset 1 (id:??) landed as
https://crrev.com/1f03256de37aaa1b1cbe81d56122defa0ad9aa9a
Cr-Commit-Position: refs/heads/master@{#28096}