This demo comes from Chromium's source repository. See the original here.
The scrollable area represents 500 "virtual" items (kNumberOfItems) using 30 "physical" DOM elements (kPhysicalCount). As elements get scrolled out of view to the top, they get moved down to the bottom via -webkit-transform: translate3d(0, NNNpx, 0) and their contents get replaced with the appropriate "virtual" item. requestAnimationFrame() is used to ensure that updates only happen once per repaint of the window.