Align HTMLAppletElement IDL with spec

http://whatwg.org/html#htmlappletelement

In addition to removing TreatNullAs=NullString, align with the spec by
making hspace/vspace unsigned long, and codebase/object URLs.

The tests for the updated properties pass in Firefox Nightly, IE11
Release Preview and Opera 12.16, with these exceptions:

IE11 returns "" after setting width/height to null and fails all of
the vspace/hspace reflection tests in ways not per spec.

Presto doesn't reflect object as a URL, but the framework didn't
notice that before the minor fix in nullTestElementAttribute.
Presto also fails the vspace/hspace set tests in ways not per spec.

BUG=316129, 310298

Review URL: https://codereview.chromium.org/64173002

git-svn-id: svn://svn.chromium.org/blink/trunk@161545 bbb929c8-8fbe-4397-9dbb-9b2b20218538