Chrome OS: hide 'Manage users' settings subpage for Child users.

This Cl also adds chrome.usersPrivate.getCurrentUser,
and removes chrome.usersPrivate.isCurrentUserOwner methods.

TBR=alemate@chromium.org

(cherry picked from commit a2c09f599ce42d7454887b062afb60f73c92c1ec)

Bug: 823534
Cq-Include-Trybots: master.tryserver.chromium.linux:closure_compilation
Change-Id: I663cb1584882cd0851474047451915fefcd3f030
Reviewed-on: https://chromium-review.googlesource.com/1072910
Commit-Queue: Alexander Alekseev <alemate@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Steven Holte <holte@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#563279}
Reviewed-on: https://chromium-review.googlesource.com/1083192
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Cr-Commit-Position: refs/branch-heads/3440@{#98}
Cr-Branched-From: 010ddcfda246975d194964ccf20038ebbdec6084-refs/heads/master@{#561733}
12 files changed