During debugging, I found it useful to hook all task creation in a
central location, and util::task was the perfect place for it.
r? @pcwalton (or maybe someone else, I'm kinda sending you a bunch of
reviews today because I don't know who better to give them to)
Source-Repo: https://github.com/servo/servo
Source-Revision: ff06be91ebe770290ba912ee71a303810aa62cea
