Doesn't cold launch in <5 seconds on benchmark hardware

1. Restart Ubuntu.
2. Simultaneously start a stopwatch and launch Ubuntu Software Center.
3. When the window appears, press Stop.

This is a sequel to bug 677088, where developers did excellent work reducing Ubuntu Software Center's warm launch time.
<http://people.canonical.com/~mvo/software-center/mini10-startup/startup-times.png>

This time, we want to improve cold launch time -- because when people run USC, most often they will run it only once before logging out. And it's likely that we've regressed since March 2011.

So, the first step is to identify benchmark hardware. Is a Dell Mini 10 still relevant? If not, what should we use instead?

Next, find some way of automating a test where Ubuntu restarts (and waits for things to settle after login) before launching USC, timing how long it takes for the window to appear, and plotting the result on a graph linked from this bug report.

Then, accelerate essential tasks -- and postpone non-essential tasks -- to reduce the cold launch time.

To be clear, this is only about the time from launching until the main window opens. So anything you can possibly postpone until after the window opens, do it. Postpone reading package state, postpone reading package installation history, postpone delay setting up a xapian database, postpone reading an icon cache, postpone everything except the minimum necessary to open the window at its correct size. Making those other tasks quicker is good, but not as good as making the window appear sooner.

<https://wiki.ubuntu.com/SoftwareCenter#Launching>: "Otherwise, the main USC window should open within five seconds on benchmark hardware."