I just synced ToT to 9f800ec0044b9c7c7c88553f406cc5e146e72516, built and tested.  VrShell 2D and WebVR have both become extremely choppy.

It looks as if pose information is being misused or corrupted, as when the device is rotated, some frames appear to be rendered at the wrong pose (like async reprojection has gone wild).

Based on syncs to ToT, I think this has been introduced in the past 2 days or so.