v8: fix tracking of longest_step in IncrementalMarking.

v8: fix tracking of longest_step in IncrementalMarking.

longest_step is only output at the end of a mark-compact. We shouldn't
reset it after a Scavenge.

R=hpayer@chromium.org
BUG=

Committed: https://code.google.com/p/v8/source/detail?r=22432

[ernstm, 2014-07-16 12:01:57]

PTAL

[Hannes Payer (out of office), 2014-07-16 12:50:26]

lgtm

[ernstm, 2014-07-16 13:07:37]

The CQ bit was checked by ernstm@chromium.org

[commit-bot: I haz the power, 2014-07-16 13:08:13]

CQ is trying da patch. Follow status at
 https://v8-status.appspot.com/cq/ernstm@chromium.org/395153003/1

[commit-bot: I haz the power, 2014-07-16 13:08:14]

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

[commit-bot: I haz the power, 2014-07-16 13:08:15]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[ernstm, 2014-07-16 13:19:38]

Committed patchset #1 manually as r22432 (presubmit successful).