Back out -webkit-overlay and just rename it back to overlay.

    Back out -webkit-overlay and just rename it back to overlay.

        Reviewed by darin

        * css/CSSComputedStyleDeclaration.cpp:
        (WebCore::CSSComputedStyleDeclaration::getPropertyCSSValue):
        * css/CSSValueKeywords.in:
        * css/cssparser.cpp:
        (WebCore::CSSParser::parseValue):
        * css/cssstyleselector.cpp:
        (WebCore::CSSStyleSelector::applyProperty):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@14968 268f45cc-cd09-0410-ab3c-d52691b4dbfc