[visualViewport]: Proposal and RFC

Hi all,

We've been working on the proposal for a visual viewport API at
https://github.com/WICG/ViewportAPI. We (Chrome) would like to ship this
feature in the nearish future but I'd like to make sure we have consensus
that this is a good idea and the current state of the proposal is
acceptable before we do so. The WICG repo has been pretty quiet so I'm
hoping to get more engagement here.

Please file issues on the GitHub repo or reply here with thoughts (good or
bad). In particular, the draft spec is pretty lacking so I'd appreciate
feedback and critiques there.

Thanks,
David