R1:04ab81aa766c

Use "webkit-overflow-scrolling" on main page scroll view

Summary: This seems to improve behavior on iOS, good call.

Test Plan: Hard to be totally sure since my local install isn't set up with a real phone, but behavior seems better on iOS simulator.

Reviewers: chad

Reviewed By: chad

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D11481