Fullscreen (distraction-free) editor should have a preview button

[markjaquith]

Per ​http://alexking.org/blog/2012/07/06/wordpress-fullscreen-preview-button

I do find it annoying to have to exit fullscreen, preview, then flip back to fullscreen.

Moving to 3.9 for consideration.

Related: #17388

This ticket was mentioned in IRC in #wordpress-dev by nacin. ​View the logs.

First pass

Doesn't quite feel right as an editor button, and that eye is still creepy. Secondary button next to update/publish?

That was my first thought as well, however when I put a secondary button the "Saved" text broke to the next line. I was also thinking about if the "Save" button was translated the space would be even tighter. Happy to give it another go if you have some suggestions for the space issue.

The DFW toolbar needs responsive styling, perhaps that can be handled there? Seems it can wrap to two lines: the Exit fullscreen, Save, Preview buttons at the top and the editor buttons at the bottom? Also "Exit fullscreen" should probably be a button.

Preview is also really tough to get right from an implementation standpoint, as it actually has to POST data under most conditions (for previewing what's currently been written, versus the last revision), versus just open up the preview URL. Alex King's hack had used the underlying preview button, which is pretty clever (at least as a hack, not suggesting that's how we should implement it).