Suppress destruction races on a pthread condvar in ThreadWatcherTest.ThreadNotResponding

BUG=308590
TBR=rtenneti@chromium.org

Review URL: https://codereview.chromium.org/136453002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244481 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244481