perfetto: Emit trace config in TraceEventMetadataSource

If tracing via the new perfetto Consumer API, TracingController won't
emit metadata. Emit the config in the TraceEventMetadataSource instead.

Bug: 950293, 950620
Change-Id: I535e6884e18a167d68788c46827b7bde43a24f8a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1559170
Commit-Queue: Eric Seckler <eseckler@chromium.org>
Auto-Submit: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#648988}
4 files changed