In Chapter 4, after Wheatley busted me out and I did a bit of running, Glados opened up the "final" test chamber and asked me to complete it. (This is the room with the heart on the wall, and you get the "good listener" achievement for entering it.) Upon entering the room, the exits all close up and the neurotoxin starts flowing.
Is there any way to escape before the neurotoxin kills me? I thought perhaps a portal could be placed outside the room before entering, but I don't see any suitable surfaces.