sync: make deferred startup contingent on sessions being enabled.

TBR=rogerta@chromium.org, kalman@chromium.org

BUG=80194

Review URL: https://codereview.chromium.org/181093002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253959 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253959
Closed UI channel for fast metro shutdown/restart.
As it works currently, when we close metro viewer with Alt+F4, the process remains in suspended state for approximately 10 seconds and terminates after that. On the browser process side, ChromeMetroViewerProcessHost class holds ref count to browser process and releases OnChannelError. With this change we trigger channel error immediately after sending Alt+F4 so that browser process can   exit/restart.

BUG=335070
R=cpu,ananta

Review URL: https://codereview.chromium.org/164553007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253960 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253960