Mac: Add default implementation for JavaScript confirm/prompt dialogs (issue #795).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef1@1041 5089003a-bbd8-11dd-ad1f-f1f9622dbc98
Linux: Improve label for JavaScript dialogs (issue #488).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef1@1043 5089003a-bbd8-11dd-ad1f-f1f9622dbc98