tracker_layout — the (semi)famous branch that rewrites Tracker to use the Layout Kit — has been merged.
This means that Tracker is no longer using the old B_FOLLOW_*-based system for resizing views, which makes for much cleaner code that's easier to read and understand. Alexandre Deckner initially did this in 2012, but due to refactors and other changes to Tracker since then, as well as some compatibility issues with his method, it wasn't possible to merge his code. After realizing this in mid-December, I started the work to move Tracker to layouts that was just merged today.
This is a companion discussion topic for the original entry at https://www.haiku-os.org/blog/waddlesplash/2015-01-27_trackerlayout_has_landed/