mash: Create and show a shelf in mash.

ui/views/mus/pointer_watcher_event_router.cc

Index: ui/views/mus/pointer_watcher_event_router.cc
diff --git a/ui/views/mus/pointer_watcher_event_router.cc b/ui/views/mus/pointer_watcher_event_router.cc
index 3df701579b6ce89e4688bff55b72f7b8b1e9aa15..6d07e1384a2ae1cfe24ed68a2c3fbb3c46495e1a 100644
--- a/ui/views/mus/pointer_watcher_event_router.cc
+++ b/ui/views/mus/pointer_watcher_event_router.cc
@@ -47,7 +47,8 @@ void PointerWatcherEventRouter::RemovePointerWatcher(PointerWatcher* watcher) {
   pointer_watchers_.RemoveObserver(watcher);
   if (!HasPointerWatcher()) {
     // Last PointerWatcher removed, stop the watcher on the window server.
-    window_tree_client_->StopPointerWatcher();
+    if (window_tree_client_)

[James Cook, 2016/08/17 03:29:39]

Where are we tearing down the window tree client before code removes its
PointerWatchers?

[msw, 2016/08/17 17:45:44]

The WindowTreeClient dtor (1) calls OnWillDestroyClient, which cleared
|window_tree_client_| (below at line 95), *then* (2) destroys windows like the
Shelf, where ShelfView's ShelfTooltipManager is a PointerWatcher, then (3) calls
OnDidDestroyClient. We should support Windows owning PointerWatcher objects, so
I changed PointerWatcherEventRouter to clear |window_tree_client_| in (3)
OnDidDestroyClient, after (2) destroying windows.

+      window_tree_client_->StopPointerWatcher();
     pointer_watcher_want_moves_ = false;
   }
 }