How to force pixels to hit the screen?

[Mike Hearn]

I'd like to create my main stage, show some splash widgets, then begin the
slower process of hauling the data and rest of the main UI into memory.
Unfortunately when I do this most of the startup time has the stage being
empty, instead of showing the splash. Introducing some artificial delays
makes it reliably appear, but of course I don't want to slow down startup.

My guess is that the app initialisation work is starving the render thread,
so the pixels for the splash don't hit the screen quickly enough. I tried
using an AnimationTimer to wait for a few pulses, but it didn't work. Ditto
for plain old runLater.

If anyone has ideas, it'd be appreciated.