Bug 1005331 - JSHint fixes for shared/js/media/

https://bugzilla.mozilla.org/show_bug.cgi?id=1005331
Totally not okay to add use strict to every function in the file just for the purpose of passing jshint.  Notice that the top-level code in the file is not in strict mode if you do it htat way.  Put a single use strict at the top of the file. Or, if you have to, wrap the whole thing in an anonymous function and export MediaFrame so that you can put a single use strict  at the top level.  This is ridiculous to have to put use strict in these two line functions.