On newest chrome we get a warning with `preventDefault()`

[petehunt]

New today I started seeing:

event.returnValue is deprecated. Please use the standard event.preventDefault() instead.

[zpao]

It's coming from this: https://github.com/facebook/react/blob/master/src/event/synthetic/SyntheticEvent.js#L82

[zpao]

Maybe we should only fall back to looking at event.returnValue if !event.preventDefault? Somebody more familiar with events would need to look.