Summary: Fixes T7033. When we've reframed the main page content we need to scroll relative to the containing frame, not relative to the window.
Test Plan:
In Safari, Chrome and Firefox, used j/k/J/K keys to navigate diff content.
Tried some other scroll-based beahviors, like jump-to-anchors.
(It looks like the highlighting reticle got slightly derped a while ago, but it's still functional, so I didn't mess with it.)
Reviewers: btrahan, chad
Reviewed By: chad
Subscribers: epriestley
Maniphest Tasks: T7033
Differential Revision: https://secure.phabricator.com/D11490
ea67a8ab8e