Many layers have no non-sRGB content.

When enabling color correct rendering, we will be rasterizing into the monitor's color space, which means doing a sRGB->monitor color conversion.

This conversion is particularly expensive when doing CPU rasterization.

If we're doing GPU compositing, then doing this conversion at draw time will be comparatively inexpensive.

This bug is to investigate identifying layers that are sRGB-only, and rasterizing them as sRGB (avoiding the image conversion), then doing the color space conversion to the monitor's color space at composite time.