Mark http/tests/workers/terminate-during-sync-operation.html as flaky.

BUG=339539
TBR=ager@chromium.org

Review URL: https://codereview.chromium.org/150613002

git-svn-id: svn://svn.chromium.org/blink/trunk@166142 bbb929c8-8fbe-4397-9dbb-9b2b20218538
In the latest WD, grid-definition-{columns|rows} were renamed to grid-template-{columns|rows}.

BUG=337626

Review URL: https://codereview.chromium.org/146773002

git-svn-id: svn://svn.chromium.org/blink/trunk@166143 bbb929c8-8fbe-4397-9dbb-9b2b20218538