Summary:
Fixes T7081. History here:
- JX.Scrollbar made the page scroll weird when a dialog came up because it was half-frame and half-document.
- I made it fully frame-level.
- But this wasn't really right; a better fix is to make it fully document-level.
Test Plan:
- Weird scroll on opening dialog is still fixed.
- iOS Safari no longer puts the mask over the dialog.
Reviewers: btrahan, chad
Reviewed By: chad
Subscribers: epriestley
Maniphest Tasks: T7081
Differential Revision: https://secure.phabricator.com/D11559
31c64b6772