Crouton in a tab

Still a few issues to iron up, more testing, and a few missing features, but the general idea is there.

Known issues:
 - The extension does not start with focus (you need to click)
 - Touch events
 - IME events
 - "Error target STRING not available" sometimes appears during switch (croutonclip/cycle?)
 - Limit number of resolution changes when resizing (it's slow because we send far too many "R" requests)
 - A leftover FIXME in the code, we should force courtoncycle instead of removing files
 - Move the websocket functions into a common file
 - Errors when loading NaCl module are not reported
I'm OK if there's effectively two implementations within a single script.  Both scripts set the resolution of the graphical chroot, so calling them both "setres" is really the way to go.  Eventually when xdummy is fixed (optimism!) the implementation will be the same.