ScrollView crashing in non-browser environments

[Joeao]

Hi Team ReactXP.

Doing some server side rendering and getting a document is not defined error. This problem seems to be similar to #730, fixed by 7e06794.

The issue can be replicated by rendering a ScrollView element in a non-browser environment. In my particular use case I'm using ReactDOMServer.renderToString, rendering a ReactXP app which includes a ScrollView.

 ReferenceError: document is not defined
    at Function.Scrollbar.getNativeScrollbarWidth (node_modules/reactxp/dist/web/CustomScrollbar.js:45:21)
    at new ScrollView (node_modules/reactxp/dist/web/ScrollView.js:147:66)

https://github.com/microsoft/reactxp/blob/master/src/web/CustomScrollbar.ts#L187
https://github.com/microsoft/reactxp/blob/master/src/web/ScrollView.tsx#L88

[fbartho]

I realize that you've fixed this in a fork of reactxp -- is this something you'd like to contribute back to core? Is there a performance implication or other risk to what you changed?