On Linux it uses GTK+, on Mac OS X Cocoa, and on Windows a custom views library, see http://www.youtube.com/watch?v=WsvNebq1dRg and also documents from http://dev.chromium.org:
- http://dev.chromium.org/developers/design-documents/chromeviews
- http://dev.chromium.org/developers/design-documents/views-windowing