State trackers are used in Gallium3D to track the state of something (such as Mesa's state) and to then translate that into operations. The Xorg state tracker deals with mode-setting, VT switching, EXA, etc. The DRI2 state tracker for the Direct Rendering Infrastructure 2 interface was completed by Jakob Bornecrantz after it was started by Keith Whitwell.
The Xorg and DRI2 state trackers for Gallium3D were added in this commit and this commit, respectively. Immediately after those were pushed into Mesa, the Intel driver was hooked in.