The WordPress views system enables live previewing of certain shortcodes while editing a post. wp.mce.views is a set of utilities that simplifies adding custom UI within a TinyMCE editor. At its core, it serves as a series of converters, transforming text to a custom UI, and back again. The WordPress audio-playlist, video-playlist, audio embeds and video embeds are examples of WordPress views.
Important: Note that Wordpress 4.2 includes a major rewrite of the wp-views as described here
wp.mce.views.register( id, view-object )
wp.mce.views is located in wp-includes/js/mce-view.js.