GitLab

This removes another use of ContentLayer in the unit tests preventing
us from deleting non-impl-side-painting code.

R=enne, vmpstr
BUG=413479
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel

Review URL: https://codereview.chromium.org/1143223006

Cr-Commit-Position: refs/heads/master@{#333188}