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Specifically, this includes metrics reported by ChromeOSMetricsProvider
in the system profile for UKM. The following fields will now be included:
- hardware.hardware_class
- hardware.internal_display_supports_touch
- hardware.bluetooth (and all the sub-fields)
- multi_profile_user_count

A note on the implementation: This reports the new short hardware class
field that is now reported to UMA (as of M67), as enabled by the kUmaShortHWClass
feature. This CL also improves this logic (both for UMA and UKM) by doing it
synchronously which is possible with the new implementation. The bluetooth data
is still retrieve asynchronously however - which is new for UKM service.

In addition, this CL fixes MetricsProvider initialization order in UkmService,
where previously the Init() call on providers was happening before providers were
added. This was not a problem before because the existing providers did not do
anything in Init().

This change also improe

Bug: 807663, 810872
Change-Id: I4b0dcb848e40a467a26feaf757f43aaf442be050
Reviewed-on: https://chromium-review.googlesource.com/996175
Commit-Queue: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549271}