ThreadSanitizer v2: suppress races during Webkit shutdown

BUG=338675
TBR=abarth@chromium.org

Review URL: https://codereview.chromium.org/136003009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@247453 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 247453