Mark media/video-frame-accurate-seek.html as flaky again

BUG=326139
TBR=mkwst@chromium.org

Review URL: https://codereview.chromium.org/305323002

git-svn-id: svn://svn.chromium.org/blink/trunk@175229 bbb929c8-8fbe-4397-9dbb-9b2b20218538