GitLab

This is a run of proto_export.py plus minimal code changes to handle
the deprecation of the ChromeUserMetricsExtension.structured_event.
A follow-up CL will update the code to use the replacement field.

The proto_export.py script also didn't delete structured_event.proto,
so I've done that manually.

Change-Id: I0ac699c1ef399674d9b3a92d41747076093f307c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2631646
Commit-Queue: Tony Yeoman <tby@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844436}