GitLab

It makes ActivityStorage customizable, so it can work with
different pref stores. For enterprise reporintg activity is
stored in local state and for consumer reporting it is kept
in user prefs.

Bug: 837001
Test: 
Run: DeviceStatusCollectorTest, ConsumerDeviceCollectorTest, UserCloudPolicyManagerChromeOSTest.
Manully: Add child account to device and observe status upload after ~60s, Sign in as child user and observe status upload after ~60s.
Change-Id: Id82d3b0d3b8a3486ceae38acf9499b6825fbbb00
Reviewed-on: https://chromium-review.googlesource.com/1056264
Commit-Queue: Aga Wronska <agawronska@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Cr-Commit-Position: refs/heads/master@{#560930}