Allow empty first parts of ConsStrings

Allow empty first parts of ConsStrings

TurboFan lowering (see [0]) of ConsString creation cannot ensure that
the first part of the cons string is non-empty without introducing a phi
and negatively impacting performance.

This modifies ConsStringIterator to allow empty first parts of
ConsStrings.

BUG=v8:5440
Committed: https://crrev.com/da27e0c88602218b3d5bdd6056d705063b1bf792
Cr-Commit-Position: refs/heads/master@{#39817}

[jgruber, 2016-09-28 09:10:29]

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

[commit-bot: I haz the power, 2016-09-28 09:10:35]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[jgruber, 2016-09-28 09:21:22]

jgruber@chromium.org changed reviewers:
+ bmeurer@chromium.org

[Benedikt Meurer, 2016-09-28 09:30:56]

LGTM, thanks.

[commit-bot: I haz the power, 2016-09-28 09:42:35]

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

[commit-bot: I haz the power, 2016-09-28 09:42:36]

Dry run: This issue passed the CQ dry run.

[jgruber, 2016-09-28 09:44:14]

The CQ bit was checked by jgruber@chromium.org

[commit-bot: I haz the power, 2016-09-28 09:44:24]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2016-09-28 09:46:43]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2016-09-28 09:47:04]

Description was changed from

==========
Allow empty first parts of ConsStrings

TurboFan lowering (see [0]) of ConsString creation cannot ensure that
the first part of the cons string is non-empty without introducing a phi
and negatively impacting performance.

This modifies ConsStringIterator to allow empty first parts of
ConsStrings.

BUG=v8:5440
==========

to

==========
Allow empty first parts of ConsStrings

TurboFan lowering (see [0]) of ConsString creation cannot ensure that
the first part of the cons string is non-empty without introducing a phi
and negatively impacting performance.

This modifies ConsStringIterator to allow empty first parts of
ConsStrings.

BUG=v8:5440

Committed: https://crrev.com/da27e0c88602218b3d5bdd6056d705063b1bf792
Cr-Commit-Position: refs/heads/master@{#39817}
==========

[commit-bot: I haz the power, 2016-09-28 09:47:05]

Patchset 1 (id:??) landed as
https://crrev.com/da27e0c88602218b3d5bdd6056d705063b1bf792
Cr-Commit-Position: refs/heads/master@{#39817}