storage/quota-tracking.html fails on snow leopard, and could potentially fail on other platforms too. The problem is that we create 3 databases at the beginning of the test, and each one of them uses some space. On the other hand, the transactions run on the first database assume that there are no other databases in this origin, and try to use more space than is available. The solution is to create databases as we go.
Created attachment 48682 [details] patch
Landed as r54853. Snow Leopard's failure seems to have been fixed.