mash: Create and show a shelf in mash.

ui/views/mus/pointer_watcher_event_router.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/views/mus/pointer_watcher_event_router.h"
 
 #include "services/ui/public/cpp/window.h"
 #include "services/ui/public/cpp/window_tree_client.h"
 #include "ui/events/base_event_utils.h"
 #include "ui/events/event.h"
@@ skipping 29 matching lines @@
   if (!had_watcher) {
     // First PointerWatcher added, start the watcher on the window server.
     window_tree_client_->StartPointerWatcher(want_moves);
   }
 }
 
 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;
   }
 }
 
 void PointerWatcherEventRouter::OnPointerEventObserved(
     const ui::PointerEvent& event,
     ui::Window* target) {
   Widget* target_widget = nullptr;
   if (target) {
     ui::Window* window = target;
@@ skipping 27 matching lines @@
 }
 
 void PointerWatcherEventRouter::OnWillDestroyClient(
     ui::WindowTreeClient* client) {
   DCHECK_EQ(client, window_tree_client_);
   window_tree_client_->RemoveObserver(this);
   window_tree_client_ = nullptr;
 }
 
 }  // namespace views