Create a wp.media.frames object

[koopersmith]

To encourage plugins to share their media frames, but not pollute the window or wp.media objects with media frame instances, let's give plugins a canonical place to put their stuff.

For example:

wp.media.frames.customHeader = wp.media();

Also, we should add wp.media.attachment( id ) as a shortcut to wp.media.model.Attachment.get( id ).

[koopersmith]

Also, adds frame caching to custom header, which works the same way as in custom background.

[nacin]

Cool.

[markjaquith]

He done been moonlighting on us!

Sure. :-) Sounds like a good idea.

[koopersmith]

In 23092:

Add a canonical location for media frames, an alias to fetch attachments, and frame caching to custom header. fixes #22775.