Fix some async repaint tests

Some async layout tests use waitUntilDone() and notifyDone() by
themselves, without setting window.testIsAsync to true.

This may be either unnecessary or incorrect, depending on which of the
test's notifyDone() and text-based-repaint.js's notifyDone() executes
first. If the latter executes first, the test may finish before it's
done causing what the test want to test not fully executed.

BUG=381242

Review URL: https://codereview.chromium.org/316193003

git-svn-id: svn://svn.chromium.org/blink/trunk@175599 bbb929c8-8fbe-4397-9dbb-9b2b20218538