ChromeOS: Add SystemTimezoneAutomaticDetection policy.

This CL adds SystemTimezoneAutomaticDetection device policy
and modifies all necessary components to support it.

BUG=596690
TEST=unittest,browsertest

Review URL: https://codereview.chromium.org/1843523002

Cr-Commit-Position: refs/heads/master@{#384768}
19 files changed