Add HTMLFormControlElement::supportsAutofocus to fix a FIXME comment.

This virtual function should return true if the form control can hanlde
'autofocucs' attribute if it is specified.

Note: HTMLInputElement::supportsAutofocus reuses InputType::isInteractiveContent
because interactiveness is required for autofocus capability.

BUG=none
TEST=none; no behavior changes.

Review URL: https://codereview.chromium.org/143343003

git-svn-id: svn://svn.chromium.org/blink/trunk@165432 bbb929c8-8fbe-4397-9dbb-9b2b20218538
void* HTMLInputElement::preDispatchEventHandler(Event* event)
{
    if (event->type() == EventTypeNames::textInput && m_inputTypeView->shouldSubmitImplicitly(event)) {
        event->stopPropagation();
        return 0;
    }
    if (event->type() != EventTypeNames::click)
        return 0;
    if (!event->isMouseEvent() || toMouseEvent(event)->button() != LeftButton)
        return 0;
    return m_inputTypeView->willDispatchClick().leakPtr();
}

void* HTMLInputElement::preDispatchEventHandler(Event* event)
{
    if (event->type() == EventTypeNames::textInput && m_inputTypeView->shouldSubmitImplicitly(event)) {
        event->stopPropagation();
        return 0;
    }
    if (event->type() != EventTypeNames::click)
        return 0;
    if (!event->isMouseEvent() || toMouseEvent(event)->button() != LeftButton)
        return 0;
    return m_inputTypeView->willDispatchClick().leakPtr();
}
