Mac: Fix nsview_additions.mm compile error

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1872 5089003a-bbd8-11dd-ad1f-f1f9622dbc98
Fix type conversion compile error (issue #1397).

git-svn-id: http://chromiumembedded.googlecode.com/svn/trunk/cef3@1874 5089003a-bbd8-11dd-ad1f-f1f9622dbc98