Do not scan the active part of the stack in oilpan conservative garbage collections.

Do not scan the active part of the stack in oilpan conservative garbage collections.

If threads are allowed to continue after safepointing there is a
stack marker. We should stop stack scanning at the marker in that
case. If there is no marker the thread whose thread we are iterating
will be blocked and we should scan all the way to the recorded
end stack pointer.

R=vegorov@chromium.org
BUG=

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=166634

[haraken, 2014-02-06 14:46:17]

LGTM.

[wibling-chromium, 2014-02-06 14:49:53]

lgtm

[Mads Ager (chromium), 2014-02-06 15:41:51]

The CQ bit was checked by ager@chromium.org

[commit-bot: I haz the power, 2014-02-06 15:41:56]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ager@chromium.org/152513006/1

[Vyacheslav Egorov (Chromium), 2014-02-06 15:57:38]

lgtm

[commit-bot: I haz the power, 2014-02-06 17:57:47]

Change committed as 166634

[abarth-chromium, 2014-02-07 16:40:36]

A revert of this CL has been created in
https://codereview.chromium.org/157593004/ by abarth@chromium.org.

The reason for reverting is: Caused
http/tests/workers/terminate-during-sync-operation.html to crash. 

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40...
.