WebKit needs toHTMLUnknownElement() and isUnknown() for sanity check.

WebKit needs toHTMLUnknownElement() and isUnknown() for sanity check.
https://bugs.webkit.org/show_bug.cgi?id=80229

Reviewed by Kent Tamura.

The code generator has naked static_cast<> which could be unsafe.
We can turn it into toHTMLUnknownElement() and the like.

No new tests. Just added a sanity check.

* dom/make_names.pl:
(printWrapperFactoryCppFile):
* html/HTMLElement.h:
(HTMLElement):
(WebCore::HTMLElement::isHTMLUnknownElement):
* html/HTMLUnknownElement.h:
(HTMLUnknownElement):
(WebCore::toHTMLUnknownElement):
(WebCore):
* mathml/MathMLElement.h:
(toMathMLElement):
* svg/SVGElement.h:
(WebCore::toSVGElement):
(WebCore):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@109702 268f45cc-cd09-0410-ab3c-d52691b4dbfc