createElementFromSavedToken shouldn't have the code to create a non-HTML element

createElementFromSavedToken shouldn't have the code to create a non-HTML element
https://bugs.webkit.org/show_bug.cgi?id=153327

Reviewed by Chris Dumez.

Since HTMLConstructionSite::createElementFromSavedToken is only used to instantiate a formatting element,
there is no need for it to support creating a non-HTML elements. Remove the branch and assert that this
is indeed the case.

createElementFromSavedToken is called in HTMLTreeBuilder::callTheAdoptionAgency and HTMLConstructionSite's
reconstructTheActiveFormattingElements. In both cases, the stack item passed to createElementFromSavedToken
is guaranteed to be in the list of active formatting elements, which only contains formatting elements.

No new tests since there is no behavioral change.

* html/parser/HTMLConstructionSite.cpp:
(WebCore::HTMLConstructionSite::insertHTMLHeadElement):
(WebCore::HTMLConstructionSite::insertHTMLHtmlStartTagBeforeHTML):
(WebCore::HTMLConstructionSite::insertFormattingElement):
(WebCore::HTMLConstructionSite::createElement): Returns Ref<Element> instead of PassRefPtr<Element>.
(WebCore::HTMLConstructionSite::createHTMLElement): Ditto.
(WebCore::HTMLConstructionSite::createElementFromSavedToken): Ditto. Removed the code to instantiate
a non-HTML element. Also assert that an element created by this function is a formatting tag.
* html/parser/HTMLConstructionSite.h:
* html/parser/HTMLTreeBuilder.cpp:
(WebCore::HTMLConstructionSite::isFormattingTag): Put into HTMLConstructionSite to add an assertion.
(WebCore::HTMLTreeBuilder::processEndTagForInBody):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@195438 268f45cc-cd09-0410-ab3c-d52691b4dbfc