Adds WindowManagerManager to mus

WindowTreeHostImpl now has a set of WindowManagerManagers. There are
two distinct modes:
. Created by way of using WindowTreeHostFactory. In this mode there is
  only one WindowManagerManager for the host.
. Created implicitly when no WindowTreeHostFactorys have been used. In
  this mode there is a WindowManagerManager per userid.

This patch doesn't enforce WindowTreeClients only created windows
under the WindowManager with the id. That'll come after
this. Additionally there is a lot of cleanup to do, but I'm trying to
minimize the extent of the changes, which are already quite large.

I've changed mash (desktop_wm) so that it no longer
uses WindowTreeHostFactory. This triggers having mus create a default
WindowTreeHost (the second mode above).

BUG=590955
TEST=covered by tests
R=ben@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1755223002

Cr-Commit-Position: refs/heads/master@{#378809}

0 files changed, 0 insertions, 0 deletions