Payment + subscription progress isn't integrated with overall progress

The payment and subscription process has a finite number of steps. Until the process is complete or failed, the Software Center Agent reports these steps to Ubuntu Software Center only as status text.

This means USC does not know how far through the process it is, so it can't present that process in a determinate way.

I suggest that the SCA report the payment steps not just as text, but also as a rough cumulative fraction of the overall time that the payment will take. For example:
0.2 Payment notification received
0.5 Preparing new software channel
1.0 Ready to install

Then, USC can show the payment and subscription process as part of the overall installation process, in a single progress bar. One portion of the progress bar can be devoted to the payment and subscription, followed by (as we already have) one portion for the download and one portion for the installation.

[Original problem reported by Jon Melamut.]

Not to be confused with bug 641437, which is about showing indeterminate progress as soon as the overall process begins.