Suppress races on extensions::InfoMap

BUG=329460
TBR=mpcomplete@chromium.org

Review URL: https://codereview.chromium.org/118093003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241536 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241536