Revert of Do not scan the active part of the stack in oilpan conservative garbage collections. (https://codereview.chromium.org/152513006/)

Reason for revert:
Caused http/tests/workers/terminate-during-sync-operation.html to crash. 

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&tests=http%2Ftests%2Fworkers%2Fterminate-during-sync-operation.html


Original issue's description:
> 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

TBR=vegorov@chromium.org,haraken@chromium.org,wibling@chromium.org,ager@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=

Review URL: https://codereview.chromium.org/157593004

git-svn-id: svn://svn.chromium.org/blink/trunk@166720 bbb929c8-8fbe-4397-9dbb-9b2b20218538