Wean WebKit from one more SPI call. We learned about this new-to-Tiger
        API from filing Radar 4433222.

        * WebView/WebHTMLView.m:
        (-[WebHTMLView _autoscroll]):
        use public CGEventSourceButtonState() instead of WKMouseIsDown() (which was using SPI internally)



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@13055 268f45cc-cd09-0410-ab3c-d52691b4dbfc