fast/parser/entity-comment-in-title.html becomes flaky with lazy attaching from the parser.

The whitespace text node at the end flakily gets rendered. This is
just an issue with our whitespace textnode handling. For now, make
the test deterministic by forcing a layout at the end of parsing.

Review URL: https://chromiumcodereview.appspot.com/23651002

git-svn-id: svn://svn.chromium.org/blink/trunk@156809 bbb929c8-8fbe-4397-9dbb-9b2b20218538