[SM Service] Service integration with metrics.

Integrates StructuredMetricsService with MetricsServiceManager and
ChromeMetricsServiceClient. Additional browser test.

BUG: crbug.com/1434483
Change-Id: Id893e27456ad489f396c61656646c4327f141e39
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4481177


Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Rohit Rao <rohitrao@chromium.org>
Commit-Queue: Andrew Bregger <andrewbregger@google.com>
Reviewed-by: Jong Ahn <jongahn@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1147418}