Only use it if no native requestAnimationFrame function is available. This should improve performance on mobile devices.
As an optimization, certain browsers (e.g. Firefox) may not execute functions sent to `requestAnimationFrame` while the window is not visible. Because our tests run in an iframe, the tests fail unless we open a popup to run the animation methods.
Animation methods get their own module, giving methods more sensible names: * `OpenLayers.Animation.requestFrame` (was `OpenLayers.Util.requestAnimationFrame`) * `OpenLayers.Animation.start` (was `OpenLayers.Util.startAnimation`) * `OpenLayers.Animation.stop` (was `OpenLayers.Util.stopAnimation`)