Clean up remaining no-longer-flakes in fast/dom.

Progress!

BUG=240515,243730
TBR=ojan

Review URL: https://codereview.chromium.org/26221006

git-svn-id: svn://svn.chromium.org/blink/trunk@159055 bbb929c8-8fbe-4397-9dbb-9b2b20218538