https://bugs.webkit.org/show_bug.cgi?id=126309

Reviewed by Andreas Kling.

To detect bad type casts, it would be good to use toHTMLFormElement() instead of
using manual type cast. Additionally FORM_ASSOCIATED_ELEMENT_TYPE_CASTS is introduced newly
to do it.

Source/WebCore:

No new tests, no behavior changes.

* html/FormAssociatedElement.h:
* html/HTMLFormControlElement.h:
* html/HTMLFormElement.cpp:
(WebCore::HTMLFormElement::submitImplicitly):
(WebCore::HTMLFormElement::validateInteractively):
(WebCore::HTMLFormElement::submit):
(WebCore::HTMLFormElement::reset):
(WebCore::HTMLFormElement::defaultButton):
(WebCore::HTMLFormElement::checkInvalidControlsAndCollectUnhandled):
(WebCore::HTMLFormElement::documentDidResumeFromPageCache):
* loader/FormSubmission.cpp:
(WebCore::FormSubmission::create):

Source/WebKit/blackberry:

* WebCoreSupport/CredentialTransformData.cpp:
(WebCore::CredentialTransformData::findPasswordFormFields):
* WebKitSupport/DOMSupport.cpp:
(BlackBerry::WebKit::DOMSupport::toTextControlElement):
* WebKitSupport/InputHandler.cpp:
(BlackBerry::WebKit::InputHandler::updateFormState):
(BlackBerry::WebKit::InputHandler::submitForm):

Source/WebKit/win:

* WebFrame.cpp:
(WebFrame::elementWithName):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@161166 268f45cc-cd09-0410-ab3c-d52691b4dbfc