There are two hosted UI modes in the VR UI:

1. A mode for dialogs, where hosted UI floats over content, and doesn't change size with content.

2. A mode for on-page popups, such as autofill, where small overlay are drawn on or near page elements.

Currently, the second mode doesn't take content's size or position into account.  This means that the autofill popup is in approximately the correct position by default, but if in fullscreen mode, or if the content is resized, the popups are misaligned.  We need to size and position the popup relative to content's position.

We might even want to specially handle an animation in content size, although they'd need special handling to avoid distorting text.

When doing this, consider both the content repositioner, and fullscreen mode.