Extract policy indicator behavior

This CL:
* Moves settings/PolicyControllable -> cr_elements/CrPolicyPrefBehavior
* Moves other pref specific behavior to CrPolicyPrefBehavior
* Extacts shared behaviors from CrPolicyIndicator into a general purpose
  behavior, CrPolicyIndicatorBehavior
* Renames CrPolicyIndicator to CrPolicyPrefIndicator

This CL should also make it easier to include just the behaviors for
Closure compilation. Otherwise it contains no functional changes,
merely does some re-factoring to prep for the addition of a network indicator
(See https://codereview.chromium.org/1369403006/ for the complete CL).

BUG=521791

Review URL: https://codereview.chromium.org/1391433003

Cr-Commit-Position: refs/heads/master@{#354417}
10 files changed