[SPv2] Add unit test for foreign layers in layer list path.

This already works, but this CL adds unit test coverage for it by cloning the
unit test for the non-layer-list path.

BUG=563667

Review-Url: https://codereview.chromium.org/2122983002
Cr-Commit-Position: refs/heads/master@{#404055}
1 file changed