[Mac][WK1] Add support for alert() in MiniBrowser.
<http://webkit.org/b/112090>

Reviewed by Anders Carlsson.

* MiniBrowser/mac/WK1BrowserWindowController.m:
(-[WK1BrowserWindowController webView:runJavaScriptAlertPanelWithMessage:initiatedByFrame:]):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145468 268f45cc-cd09-0410-ab3c-d52691b4dbfc