Valgrind Mac: Put a suppression back in for a sporatic leak.

BUG=31634
TEST=none
TBR=jhawkins
Review URL: http://codereview.chromium.org/6759078

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@80214 0039d316-1c4b-4281-b951-d872f2087c98