Add a test for subclass maps.
Add a test for subclass maps.

R=arv@chromium.org

Review URL: https://codereview.chromium.org/1052963002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#27812}

UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh,UniversalFuture/moosh