Reviewed by Dimitri Glazkov.

        https://bugs.webkit.org/show_bug.cgi?id=36387
        REGRESSION: Can "uncheck" radio buttons by clicking on them

        My change in r56174 caused radio buttons and checkboxes to go down the same code path by virtue
        of allowsIndeterminate(), but this broke save/restore behavior on radio buttons.

        Fix by saving and restoring both the intermediate and checked state for radio buttons
        and checkboxes, as well as the "current radio button" state.

        Test: fast/forms/radio-checkbox-restore-indeterminate.html

        * html/HTMLInputElement.cpp:
        (WebCore::EventHandlingState::EventHandlingState): New struct to hold state between preDispatchEventHandler()
        and postDispatchEventHandler().
        (WebCore::HTMLInputElement::preDispatchEventHandler): Store intermedate and checked state
        and the current radio button.
        (WebCore::HTMLInputElement::postDispatchEventHandler): Restore state as appropriate.
        * html/HTMLInputElement.h: Add a comment to clarify how 'intermediate' interacts with 'checked', according
        to the spec.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@56284 268f45cc-cd09-0410-ab3c-d52691b4dbfc