GitLab

Initial attempt found here: https://codereview.chromium.org/983933002/

This is going to be used by https://codereview.chromium.org/975943002/

TEST=LayerOwnerTest.RecreateRootLayerWithNullCompositor
TEST=LayerOwnerTestWithCompositor.RecreateRootLayerWithCompositor

BUG=337596

Review URL: https://codereview.chromium.org/987043004

Cr-Commit-Position: refs/heads/master@{#319665}