This ensures that we have gatekeepers for API changes.

R=adamk@chromium.org

Change-Id: I7a78f9590dfc444a20044fe323b9470f4f9004a3
Reviewed-on: https://chromium-review.googlesource.com/986267
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52318}