Gardening: fast/files/workers/worker-read-blob-async-crash.html flaky

BUG=353208
TEST=
TBR=zmo@chromium.org

Review URL: https://codereview.chromium.org/202243004

git-svn-id: svn://svn.chromium.org/blink/trunk@169377 bbb929c8-8fbe-4397-9dbb-9b2b20218538