Fix a harmless data race in Thread
Fix a harmless data race in Thread

Currently, if StopSoon/Stop is called twice (like in ThreadTest.StopSoon) message_loop_ can be accessed simultaneously by ThreadMain():162 and in StopSoon():124.
This data race is harmless since stopping_==true, so message_loop_ value is actually un-needed.

I'd like to swap the conditions to avoid reading message_loop_ in case stopping_==true.
This way ThreadTest.StopSoon will have no race reports under ThreadSanitizer. Currently, this is the only report on base_unittests on ThreadSanitizer linux bot.
Review URL: http://codereview.chromium.org/207039

git-svn-id: http://src.chromium.org/svn/trunk/src@26691 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

Former-commit-id: 43ee28d2b4911cebf24bd1d23a12333922c29f3a
meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser,meego-tablet-ux/meego-app-browser