The Chrome OS team uses a cool robot built by the Finnish company OptoFidelity to measure end-to-end latency of Android and Chrome OS devices
Video below captured by a high speed video camera shows you how drawing a line on a screen is actually drawn in segments that fade in slowly.
Touchbot source code is open-source and available for everyone at https://chromium.googlesource.com/chromiumos/platform/touchbot
You can even go to http://crostouchlatency.appspot.com
to play with all latency tests.