Add suppression: JSON-strigify.html test is keeping DEPS bot failing.

TBR=cbiesinger
BUG=14885
BUG=306929

Review URL: https://codereview.chromium.org/189363004

git-svn-id: svn://svn.chromium.org/blink/trunk@168702 bbb929c8-8fbe-4397-9dbb-9b2b20218538