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Per discussions with product and legal, we want to continue to use a
single metrics reporting / crash upload consent on Chrome OS, for both
the OS and the lacros browser. Notes at go/lacros-crash-consent

Per design doc at go/lacros-metrics-consent, the initial value is
sent as part of LacrosInitParams, which is available early in lacros
startup. Lacros then registers itself over mojo as an observer for
future changes. The observer is fired immediately when added to avoid
a possible race condition.

Future CLs will implement:
* lacros -> ash communication if the user disables metrics in browser
  settings
* Better interactions with device vs. user policy controls

Bug: 1148604, 1143851
Test: added to unit_tests and lacros_chrome_browsertests

Change-Id: Ib6431d33acab6cb8d4e95584a7d95288dc52ea27
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2570045Reviewed-by: Jorge Lucangeli Obes <jorgelo@chromium.org>
Reviewed-by: Erik Chen <erikchen@chromium.org>
Commit-Queue: James Cook <jamescook@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834531}