Remove some unreliable usages of setTimeout( ,0) from layout tests

These are flaky after https://codereview.chromium.org/467153003, which
made a 0ms setTimeout() no longer be a minimum 1ms delay.

These tests all depend on doing work during or after the load event, but
attempt to do so in ways that aren't strictly guaranteed to meet that
requirement.

BUG=

Review URL: https://codereview.chromium.org/733633003

git-svn-id: svn://svn.chromium.org/blink/trunk@185398 bbb929c8-8fbe-4397-9dbb-9b2b20218538