Grid steals focus during browser blur event because document.activeElement is set to body in Chrome

[supamanda]

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WHICH VERSION OF REACT ARE YOU USING?

Officially Supported:
[ ] v0.14.x

Community Supported:
[x ] v15.0.x

WHICH BROWSER ARE YOU USING?

Officially Supported:
[ ] IE 9 / IE 10 / IE 11
[ ] Edge
[x ] Chrome

Should work:
[ ] Firefox
[ ] Safari

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I'm submitting a ... (check one with "x")

[x ] bug report
[ ] feature request
[ ] support request => Please do not submit support request here, instead see https://github.com/adazzle/react-data-grid/blob/master/CONTRIBUTING.md

Current behavior
According to https://developer.mozilla.org/en-US/docs/Web/Events/blur,
Note: The value of Document.activeElement varies across browsers while this event is being handled (bug 452307): IE10 sets it to the element that the focus will move to, while Firefox and Chrome often set it to the body of the document.

Cell checkFocus() will steal focus if it has been selected and the focus is on the body - which may have happened during an onblur event.

Expected/desired behavior
The comment says:
Only focus to the current cell if the currently active node in the document is within the data grid.

The body is not within the data grid, so maybe it would be better not to autofocus when it is focused on the body.

Reproduction of the problem
If the current behavior is a bug or you can illustrate your feature request better with an example, please provide the steps to reproduce and if possible a minimal demo of the problem.

I've set up a sample that demonstrates the problem: see https://fiddle.jshell.net/supamanda/hLexpyx8/

What is the expected behavior?

What is the motivation / use case for changing the behavior?