GitLab

This CL moves the GPU-related system profile metrics logging out of MetricsLog
into GPUMetricsProvider, which is a metrics::MetricsProvider. A new unittest is
created to provide the related test coverage that was previously provided in
the MetricsLog unittest.

BUG=374228
R=asvitkine@chromium.org, isherman@chromium.org

Review URL: https://codereview.chromium.org/291163006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@272484 0039d316-1c4b-4281-b951-d872f2087c98