ResizeObserver sometimes provides list with an invalid size

[niik]

Reported by @shiftkey

And seen by donokuda

When @shiftkey saw it he also reported that the tab bar in the sidebar was squished

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I have not been able to reproduce this yet but looking at these screenshots it's pretty clear that what's happening is that the list is not auto-sizing correctly which means that this is very likely a bug related to us ditching react-virtualized's AutoSizer component for ResizeObserver in #1126.

The fact that @donokuda's screnshot shows the foldout rendering underneath the toolbar item is also highly interesting although I'm not able to draw any conclusions based on that just yet.

I imagine that the squished tab bar that @shiftkey was seeing is also related to the resize observer giving the file list an invalid height. When I artificially add an some extra height to the list I'm able to get the same behavior

What we know

• Both @shiftkey and @donokuda is running the app in a Windows VM from their 🍎 💻

Theories

• High-dpi?
• Race condition with the resize observer callback

[niik]

Bingo, I'm able to reproduce this when running at 200% DPI

Seems like the resize observer is not taking scaling into account somehow