We get away with this on iOS because the devices are just faster, but on Android it's very slow, e.g. 1ms on a 6ms raster frame for this code in the old gallery on a Samsung tablet: https://github.com/flutter/engine/blob/942909b77001b4904e26aa29e3cac63345108a0a/shell/gpu/gpu_surface_vulkan_impeller.cc#L69-L82

I have a large WIP patch that changes things around so most of this work is done on the UI thread instead and it seems promising. It is too rough to get good numbers from right now but filing this bug to track work on that. This should improve both Vulkan and GL on Android, and offer some smaller improvement for Metal on iOS/Desktop.