1) Chromeos doesn't allow an end-user to set a proxy on the version of chrome shipped with the chromebook.

2) If the end user is running some other browser they had to install it via crouton or by installing another distro on their chromebook.

2a) In either case, the user can simply install TBB.

3) There is no need to make a chromebook-specific package. In fact, I don't think it is possible to make one.