Use case

Given the same aspect ratio, I would like my applications to look the same on my embedder, regardless of the actual size of the window. The pixel ratio is exposed as part of the FlutterWindowMetricsEvent struct, but no way to set it explicitly is provided as part of the desktop embedder (I'm working on Linux specifically).

Proposal

It should be fairly straightforward to pass in the pixel ratio to the FlutterWindow, maybe as part of the WindowFrame passed in SetFrame() or as its own new method.
Currently it seems that the pixel ratio is used to deal with non-standard monitor resolutions, so that might make the change nontrivial.