Introduce API in ui::Layers for setting rounded corners

This patch adds an API to ui::Layers that lets clients set a rounded
corner radius on the layer. The change is propagated to the cc layer
and its effect node as well.

Adds unit test for the change.

Bug: 903486
Change-Id: Ib0d36af9e76b9f6701e0cb674e855e29f5844c7f
Component: ui layer, cc layer, effect node
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1497851
Commit-Queue: Malay Keshav <malaykeshav@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: enne <enne@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637572}
6 files changed