Metal: Auto detect parent layer's contentsScale change Currently when user passes a CALayer to create WindowSurface, Metal back-end will create a child CAMetalLayer to render to. However, when this CALayer's contentsScale is changed, the CAMetalLayer's contentsScale wasn't updated accordingly. This CL fix this. Bug: angleproject:2634 Change-Id: I20411aa8b81a30c6353e595680f1de00a4a24da7 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2482407 Reviewed-by: Jamie Madill <jmadill@chromium.org> Commit-Queue: Le Hoang Quyen <le.hoang.q@gmail.com>