Gardening: virtual/threaded/animations/import.html times out randomly

On linux and windows

BUG=353790
TEST=
TBR=zmo@chromium.org

Review URL: https://codereview.chromium.org/203483006

git-svn-id: svn://svn.chromium.org/blink/trunk@169497 bbb929c8-8fbe-4397-9dbb-9b2b20218538