GitLab

While working on issue 410276, in particular in
https://codereview.chromium.org/542733002/ , I had to update the
tracing cache backend. Why? Does anyone use it?

Let's remove it instead.

R=pasko@chromium.org,clamy@chromium.org
BUG=None

Review URL: https://codereview.chromium.org/544923002

Cr-Commit-Position: refs/heads/master@{#293505}