Have WindowTreeClient detect error state earlier

ui/views/mus/pointer_watcher_event_router.h

 // 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.
 
 #ifndef UI_VIEWS_MUS_POINTER_WATCHER_EVENT_ROUTER_H_
 #define UI_VIEWS_MUS_POINTER_WATCHER_EVENT_ROUTER_H_
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/observer_list.h"
@@ skipping 53 matching lines @@
   void AttachToCaptureClient(aura::client::CaptureClient* capture_client);
   void DetachFromCaptureClient(aura::client::CaptureClient* capture_client);
 
  private:
   friend class PointerWatcherEventRouterTest;
 
   // Determines EventTypes based on the number and type of PointerWatchers.
   EventTypes DetermineEventTypes();
 
   // aura::WindowTreeClientObserver:
-  void OnDidDestroyClient(aura::WindowTreeClient* client) override;
+  void OnWillDestroyClient(aura::WindowTreeClient* client) override;
 
   // aura::client::CaptureClientObserver:
   void OnCaptureChanged(aura::Window* lost_capture,
                         aura::Window* gained_capture) override;
 
   aura::WindowTreeClient* window_tree_client_;
   // The true parameter to ObserverList indicates the list must be empty on
   // destruction. Two sets of observers are maintained, one for observers not
   // needing moves |non_move_watchers_| and |move_watchers_| for those
   // observers wanting moves too.
   base::ObserverList<views::PointerWatcher, true> non_move_watchers_;
   base::ObserverList<views::PointerWatcher, true> move_watchers_;
 
   EventTypes event_types_ = EventTypes::NONE;
 
   DISALLOW_COPY_AND_ASSIGN(PointerWatcherEventRouter);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_MUS_POINTER_WATCHER_EVENT_ROUTER_H_