This was found while trying to fix
https://github.com/glfw/glfw/issues/1169

VulkanSurfaceMtl and metal/SurfaceMtl already handle contentsScale
correctly.

Change-Id: I234d7b0901dd7c075cf1e9d58466f52140ab1e2b
Bug: None
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2154670Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Commit-Queue: Corentin Wallez <cwallez@chromium.org>