`wp.media` now recognizes the `frame` attribute (currently a string; either'select' or 'post') and defaults to using a basic select frame. It also checks for the existence of classes in a safer fashion, as it does not assume the `MediaFrame` property exists.
see #21390.
git-svn-id: http://core.svn.wordpress.org/trunk@22495 1a063a9b-81f0-0310-95a4-ce76da25c4cd