Ask HN: Why has Chrome's rendering performance got so bad?

Chrome's rendering performance on high res displays is absolutely abysmal. Both on a brand new 13" retina Macbook Pro and my Core i7, high spec Nvidia card Windows desktop with a 4K monitor are dreadful. I get checkerbox rendering when scrolling and horrible repainting.

Safari and Firefox have none of these issues. I've had a look on the Chromium bug tracker but the ones that seem relevant say 'fixed'. Any ideas of how to improve this?