added test suppression: timeout in http/tests/media/media-source/mediasource-play.html

BUG=278400
TBR=jianli@chromium.org

Review URL: https://codereview.chromium.org/22861038

git-svn-id: svn://svn.chromium.org/blink/trunk@156649 bbb929c8-8fbe-4397-9dbb-9b2b20218538