Make UserManager a non-Lazy singleton
This CL turns the UserManager from a LazyInstance singleton with an
unpredictable lifetime into a singleton that is explicity instantiated
and torn down at well-defined points in the browser's lifetime.
BUG=None
For tests that need to instantiate a UserManager now:
TBR=oshima,hashimoto,mnissler,benwells,davemoore,pkotwicz,sky
Review URL: https://chromiumcodereview.appspot.com/
14362029
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@195501 0039d316-1c4b-4281-b951-d872f2087c98