[SyncFS] Respect sync_enabled_ flag on sync status

BUG=

Review URL: https://codereview.chromium.org/187563003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@255053 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 255053