The `canPlayType` property for audio and video in JS is so bad that the official valid responses are "probably" and "maybe". There are many cases where we might want to know if an audio|video tag is gonna blow up in our face before even attempting to make a `MediaElementPlayer` instance out of it.

The best (and most cautious) way to tackle this is to whitelist types by browser. Imagine that one implemented MEjs in TinyMCE's rich editor mode, this would be very helpful.

Add `isCompatible( $media )` to `wp.media.mixin`. Future features will use this.

See #27389.



git-svn-id: https://develop.svn.wordpress.org/trunk@27539 602fd350-edb4-49c9-b593-d223f7449a82