sync: reland deferred init

TBR=nyquist@chromium.org
BUG=80194,348951

Review URL: https://codereview.chromium.org/183563004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255890 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255890