Move AppsListViewDelegate away from listening to Signin notifications.

As part of eliminating Signin notifications in favor of observing the
SigninManager, this CL moves AppsListViewDelegate from listening to Signin
notifications to observing SigninManagers. As AppsListViewDelegate needs to get
information on signin-related events from all SigninManagers,
AppsListViewDelegate also observes SigninManager creation and shutdown via the
SigninManagerFactory (following the pattern established by
https://codereview.chromium.org/132743004/).

BUG=333997

Review URL: https://codereview.chromium.org/169393003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@254747 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 254747