ChromeOS: Add SystemTimezoneAutomaticDetection policy.

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

BUG=596690
TEST=unittest,browsertest

Committed: https://crrev.com/fc3524a0efece0f2b55b08980b74c23be65ed8dd
Cr-Commit-Position: refs/heads/master@{#384768}

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

Cr-Commit-Position: refs/heads/master@{#385157}
19 files changed