https://bugs.webkit.org/show_bug.cgi?id=108248

Reviewed by Dimitri Glazkov.

The only reason willAddAuthorShadowRoot exists is so that a handful of
other elements can create the user agent shadow root right before the
author shadow root is created. Instead of providing this generic hook
just expose a virtual method on Element that requests this behavior.

No new tests, just refactoring.

* dom/Element.cpp:
(WebCore::Element::createShadowRoot):
* dom/Element.h:
(Element):
(WebCore::Element::alwaysCreateUserAgentShadowRoot): Added.
* dom/ElementShadow.cpp:
(WebCore::ElementShadow::addShadowRoot): Remove willAddAuthorShadowRoot notification.
* html/HTMLButtonElement.cpp:
* html/HTMLButtonElement.h:
* html/HTMLFormControlElement.cpp:
* html/HTMLFormControlElement.h:
* html/HTMLMediaElement.cpp:
* html/HTMLMediaElement.h:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@141292 268f45cc-cd09-0410-ab3c-d52691b4dbfc