Popover getPositioningStyle doesn't respect anchorEl's parent window

[ianschmitz]

• I have searched the issues of this repository and believe that this is not a duplicate.

Expected Behavior

The Popover doesn't overflow the anchorEl parent window when being positioned.

Current Behavior

Popover.getPositioningStyle contains logic to position the popover relative to the anchorEl prop. It currently uses the global window object to get the innerHeight and innerWidth when calculating if the Popover is overflowing the window:
https://github.com/mui-org/material-ui/blob/c3afd7bb33fa26e465dc333449e9449a4bb9e7bd/src/Popover/Popover.js#L123-L125

The problem above is that it is referencing the global window object when performing its position calculations, instead of the parent window of the anchorEl prop. A quick fix for this could be to use Node.ownerDocument.defaultView if an anchorEl was provided, which returns the Window object.

Steps to Reproduce (for bugs)

See https://codesandbox.io/s/6lqo45vzvk. You can see that the menu is positioned correctly within the main window relative to the button, however in the popout window the menu overflows the parent window.

Context

After testing the rewrite of the Portal component following my previous issue #9207, I noticed the Popover positioning issue within the second window.

Your Environment

Tech	Version
Material-UI	1.0.0-beta.30
React	16
browser	all
etc