I just found this while flipping through Armor Games, it's the flash version of Portal. It's not first person like the Valve game, but its just as fun.
"We don't just borrow words; on occasion, English has pursued other languages down alleyways to beat them unconscious and rifle their pockets for new vocabulary." — James D. Nicoll
The Flash version seems to have a lot of annoying control issues. Why are the portals created in a weird order? Why can't I just right-click? I'm pretty sure I should have landed on that platform.
I'd take the real thing over it any day, but it was a fun diversion.
While you're on the top ledge, put both portals on the floor. Hop in one, the momentum will send you up high enough to shoot a portal over the barrier. Bounce from behind the barrier to the other side, but make sure the blue lights aren't on to fry you. Then just jump over to the exit.