[GSoC 2018] Implement a single updater class for Dominators

Hello,

My proposal for GSoC 2018 on implementing a single updater class for
Dominators [1] was accepted.

This summer, I’ll work with my mentor Jakub Kuderski on implementing a new
uniform API for Dominators and I will try to make incremental updates
faster on that basis.

Thanks,

Chijun Sima

[1]