Attempt to de-flakify http/tests/history/back-to-javascript-url-iframe.html

I got sloppy and used a setTimeout(,25) when I initial wrote it. This changes to
a setTimeout(,0) in the child frame, which appears to be pretty reliable in
getting the test to actually finish.

Tested with blink r158550 reverted to verify that this still crashes and is
therefore still a valid regression test.

BUG=317772

Review URL: https://codereview.chromium.org/62103011

git-svn-id: svn://svn.chromium.org/blink/trunk@161950 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Various cleanups in element creation code

Use HashMap<AtomicString> in the element factories, remove unnecessary forward-declarations
in the factories, and fix up QualifiedName assertion in Document::createElement.

R=abarth@chromium.org

Review URL: https://codereview.chromium.org/71093002

git-svn-id: svn://svn.chromium.org/blink/trunk@161951 bbb929c8-8fbe-4397-9dbb-9b2b20218538