Revert of DevTools: Stop collecting async stacks while profiling. (https://codereview.chromium.org/257453005/)

Reason for revert:
Speculative revert. It may have made the following
layout test flaky:
inspector/profiler/cpu-profiler-profiling.html

See flakiness dashboard:
http://build.chromium.org/f/chromium/perf/dashboard/ui/changelog_blink.html?url=%2Ftrunk&range=172750%3A172770&mode=html

Original issue's description:
> DevTools: Stop collecting async stacks while profiling.
> 
> BUG=367135
> R=pfeldman, yurys, sergeyv
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=172762

TBR=pfeldman@chromium.org,sergeyv@chromium.org,yurys@chromium.org,aandrey@chromium.org
NOTREECHECKS=true
NOTRY=true
BUG=367135

Review URL: https://codereview.chromium.org/264743005

git-svn-id: svn://svn.chromium.org/blink/trunk@173072 bbb929c8-8fbe-4397-9dbb-9b2b20218538