In order to run this demo, you will need:
An up-to-date version of Chrome, at least version 61 or newer
A USB DFU class device
For a WebUSB friendly USB DFU bootloader that can be flashed onto inexpensive STM32F103 boards, check out the dapboot project.
Some recent STM32 parts have on-chip USB DfuSe bootloaders that are supported by this site.