We're too early in the port to have incorporated a toolkit. Most of the custom drawing goes through a library called Skia, which is comparable to Cairo in that it draws lines and rectangles but not buttons and checkboxes.
Many people have strong opinions about the toolkit, and part of the reason it's so divisive is because both libraries are quite capable of meeting Chromium's needs. In fact, because most of Chromium is just custom rendering for showing a web page -- for example, even the popup of an HTML
