TimeClip converts -0 to +0, following ES2015 spec

TimeClip converts -0 to +0, following ES2015 spec

In ES2015, section 20.3.1.15, TimeClip (an internal algorihtm which is
called when normalizing Date representations) is specified to add 0
to its result, which converts -0 into +0. This patch adds that conversion
to the Date code. It is verified by the test262 test
built-ins/Date/TimeClip_negative_zero

R=adamk

Committed: https://crrev.com/eeaf80cd86513c145b8c9dd195dde3912abf4585
Cr-Commit-Position: refs/heads/master@{#31159}

[Dan Ehrenberg, 2015-10-07 01:24:19]

The CQ bit was checked by littledan@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-10-07 01:24:25]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1387293002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1387293002/1

[commit-bot: I haz the power, 2015-10-07 01:46:37]

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

[commit-bot: I haz the power, 2015-10-07 01:46:38]

Dry run: This issue passed the CQ dry run.

[adamk, 2015-10-07 18:13:49]

The CQ bit was checked by adamk@chromium.org

[adamk, 2015-10-07 18:13:50]

lgtm

[commit-bot: I haz the power, 2015-10-07 18:14:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1387293002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1387293002/1

[commit-bot: I haz the power, 2015-10-07 18:17:52]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-07 18:19:09]

Patchset 1 (id:??) landed as
https://crrev.com/eeaf80cd86513c145b8c9dd195dde3912abf4585
Cr-Commit-Position: refs/heads/master@{#31159}