Remove app banners from about:flags

Didn't finish for M34, hiding the flag for the cut.

BUG=341556

Review URL: https://codereview.chromium.org/162833002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251043 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251043
Add avatar syncing for supervised users.

When the supervised user changes his avatar, the change is
synced to his other devices, as well as to the settings of
the custodian who sees the updated avatar when opening the
supervised user import overlay.

BUG=339060
TEST=unit_tests

Review URL: https://codereview.chromium.org/147083016

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251044 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251044