TestExpectations: fast/mediastream/RTCPeerConnection-stats.html is failing

BUG=282620
TBR=tommyw@chromium.org

Review URL: https://codereview.chromium.org/23604015

git-svn-id: svn://svn.chromium.org/blink/trunk@157013 bbb929c8-8fbe-4397-9dbb-9b2b20218538