Fix border radius on composited children.
When a child of an overflow: hidden object is composited (and the ancestor is not) we were failing to apply the border-radius clip. This patch fixes the problem by adding a new masking layer for this situation, and modifying the layers used for painting to set the clip appropriately.
New tests are added to verify the behavior for border styles, and existing layout tests cover the bug (and fail before this patch). Unit testing is used for verifying update behavior.
There are remaining issues tracked in TODOs with corresponding bugs.
BUG=157218
CQ_INCLUDE_TRYBOTS=master.tryserver.chromium.linux:linux_layout_tests_slimming_paint_v2
Review-Url: https://codereview.chromium.org/2194273002
Cr-Commit-Position: refs/heads/master@{#437948}
30 files changed
