Checking why we don't get HW overlays for non integer scale-factors we noticed that quads display_rects might have subpixel position/size.

KMS supports subpixel positioning for planes (with fixed point), but Chrome rejects them.
Chrome overlay APIs seem to be using gfx::Rect instead of a gfx::Rectf for overlays rects in many places.

If we want to use HW overlays in more scenarios, we should change the APIs to use gfx::Rectf, or we need to make sure that quads are aligned to the display pixel grid.