[Cellular] Add metrics for activation status and time to connected.

This CL adds metrics to track the cellular activation status on login
and time to connected for cellular network.

Bug: 951528
Change-Id: I6498be68213ed41168170ac30186732c02851f0a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1576500
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Commit-Queue: Azeem Arshad <azeemarshad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654285}
5 files changed