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..3696acb569d9790f9d252922d373c733633ee23d 100644
--- a/ui/views/mus/pointer_watcher_event_router.cc
+++ b/ui/views/mus/pointer_watcher_event_router.cc
@@ -44,6 +44,7 @@ void PointerWatcherEventRouter::AddPointerWatcher(PointerWatcher* watcher,
 }
 
 void PointerWatcherEventRouter::RemovePointerWatcher(PointerWatcher* watcher) {
+  DCHECK(pointer_watchers_.HasObserver(watcher));

[James Cook, 2016/08/17 18:31:50]

FYI - We'll have to see how this goes. I vaguely remember seeing some code that
could attempt to remove the same PointerWatcher twice. That said, removing twice
seems like a dumb thing to do, so I support the DCHECK.

[msw, 2016/08/17 18:55:17]

Acknowledged.

   pointer_watchers_.RemoveObserver(watcher);
   if (!HasPointerWatcher()) {
     // Last PointerWatcher removed, stop the watcher on the window server.
@@ -87,8 +88,9 @@ void PointerWatcherEventRouter::OnWindowTreeCaptureChanged(
   FOR_EACH_OBSERVER(PointerWatcher, pointer_watchers_, OnMouseCaptureChanged());
 }
 
-void PointerWatcherEventRouter::OnWillDestroyClient(
+void PointerWatcherEventRouter::OnDidDestroyClient(
     ui::WindowTreeClient* client) {
+  DCHECK(!pointer_watchers_.might_have_observers());

[sky, 2016/08/17 19:50:36]

I suspect we'll have to remove this, but we can try it. My concern is that
PointerWatcherEventRouter::OnDidDestroyClient may be called before other places
do their cleanup.

   DCHECK_EQ(client, window_tree_client_);
   window_tree_client_->RemoveObserver(this);
   window_tree_client_ = nullptr;