Consider integrating InputDeviceCapabilities

[RByers]

The sourceCapabilities property of UIEvent was incubated in the WICG. If this API becomes successful (eg. widely used by developers / implemented in more than one browser), then we should consider transitioning it out of incubation and into this spec.

[RByers]

FWIW for the last 2 years we've seen about 0.6% of page loads in Chrome (i.e. a HUGE number) calling InputDeviceCapabilities#firesTouchEvents. To me, this confirms our hypothesis that the API is addressing a real, but somewhat niche, problem for developers. In particular, it's only necessary for UI which aims to have a good experience on devices where the user commonly uses both a touchscreen and mouse input device. This isn't likely very relevant anywhere WebKit runs, but should potentially be relevant for Gecko on some Windows laptops.

We consider this API successful in chromium and would again be happy to invest in migrating the specification to a WG if there was interest from another implementer.