Sync metrics protos with google3

Bug: 851163
Change-Id: I70938c74d799ca1377d2d368ed0be28090f1ad1f
Reviewed-on: https://chromium-review.googlesource.com/1180527
Commit-Queue: Mike Wittman <wittman@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584591}
7 files changed