Make fast/forms/time-multiple-fields/time-multiple-fields-focus.html work when the parser lazy attaches

autofocus doesn't happen until an element attaches which means that we need to
trigger a recalc style in this test before looking at the activeElement.

BUG=276687

Review URL: https://chromiumcodereview.appspot.com/23038016

git-svn-id: svn://svn.chromium.org/blink/trunk@156512 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Introduce toHTMLFrameElementBase and use it.

BUG=none
TEST=none; no behavior changes.

Review URL: https://chromiumcodereview.appspot.com/22851008

git-svn-id: svn://svn.chromium.org/blink/trunk@156513 bbb929c8-8fbe-4397-9dbb-9b2b20218538