gpu_cache.rs example doesn't handle the case where window is moved to a screen with different DPI factor at runtime

Created by: mitchmindtree

I noticed this when moving the window from my regular monitor (DPI of 1.0) to my retina MBP (DPI of 2.0). It's not a big issue, but it'd be nice to demonstrate the correct handling of this case. I can imagine many users will copy this example directly for their own code!

This is what it looks like when the example is run and opened on my regular monitor:

This is what it looks like when first dragged from my regular monitor to my retina display:

Once I resize it very slightly (a pixel or two) it seems to trigger a redraw, but at the original size without consideration of the new DPI factor:

This is what it looks like when opened initially on my retina display: