Disambiguate `this` and use the `@this` annotation in `media-editor.js`. This will become way more necessary in other places, but a few examples here show how confusing it can be. 

See #26870.



git-svn-id: https://develop.svn.wordpress.org/trunk@26989 602fd350-edb4-49c9-b593-d223f7449a82
Remove debug cruft.

Props nacin.
See #26870.



git-svn-id: https://develop.svn.wordpress.org/trunk@26990 602fd350-edb4-49c9-b593-d223f7449a82