Only show Data Saver usage data since enabled if less than 30 days

Includes some refactoring in how the network stats data is reconciled
with time of day for presenting day labels. The previous TimeZoneOffset
approach really didn't work and that became apparent when charting
a single day.

Bug: 820286
Change-Id: If14b456aaef6ae5729a9292842364f4115d0a563
Reviewed-on: https://chromium-review.googlesource.com/1111080
Reviewed-by: Ben Greenstein <bengr@chromium.org>
Reviewed-by: Theresa <twellington@chromium.org>
Commit-Queue: Doug Arnett <dougarnett@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576596}
5 files changed