Thanks, how could I not notice this… Compiz is now built (for trusty)
in ppa:mitya57/gnome-test — for those who want to test it.
You now need to apply something like
http://bazaar.launchpad.net/~mitya57/compiz/port-gtk-window-decorator-to-gtk3/revision/3862
to your branch, so that it could pass upstream CI tests. Also, you
should bump metacity build-dependency to whatever will be the next
version number.