virtual/threaded/animations/transition-and-animation-1.html is flaky.

BUG=352405
TBR=zmo@chromium.org

Review URL: https://codereview.chromium.org/197923007

git-svn-id: svn://svn.chromium.org/blink/trunk@169174 bbb929c8-8fbe-4397-9dbb-9b2b20218538