`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: https://develop.svn.wordpress.org/trunk@22495 602fd350-edb4-49c9-b593-d223f7449a82