Add conversions for disallowed intervals from ListValue

Add parsers to convert Value types into WeeklyTimeIntervals. Will be
used to decode DeviceAutoUpdateTimeRestrictions from its JSON string.

BUG=chromium:852860
TEST=unit tests

Change-Id: I2d1151c0e36d52b070e05a20852b8ec3f9603505
Reviewed-on: https://chromium-review.googlesource.com/1121626
Commit-Queue: Adolfo Higueros <adokar@google.com>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573018}
4 files changed