Replace WmWindowObserver with aura::WindowObserver.

ash/common/wm_window.h

Index: ash/common/wm_window.h
diff --git a/ash/common/wm_window.h b/ash/common/wm_window.h
index c855661f902b67cd19c6e587a1ee52847684bdd6..078dd0172720da33d1f678d4050b2f76a82817b5 100644
--- a/ash/common/wm_window.h
+++ b/ash/common/wm_window.h
@@ -49,7 +49,6 @@ class RootWindowController;
 class WmLayoutManager;
 class WmShell;
 class WmTransientWindowObserver;
-class WmWindowObserver;
 class WmWindowTestApi;
 enum class WmWindowProperty;
 
@@ -354,10 +353,6 @@ class ASH_EXPORT WmWindow : public aura::WindowObserver,
   // Returns a View that renders the contents of this window's layers.
   std::unique_ptr<views::View> CreateViewWithRecreatedLayers();
 
-  void AddObserver(WmWindowObserver* observer);
-  void RemoveObserver(WmWindowObserver* observer);
-  bool HasObserver(const WmWindowObserver* observer) const;
-
   void AddTransientWindowObserver(WmTransientWindowObserver* observer);
   void RemoveTransientWindowObserver(WmTransientWindowObserver* observer);
 
@@ -376,20 +371,9 @@ class ASH_EXPORT WmWindow : public aura::WindowObserver,
   explicit WmWindow(aura::Window* window);
 
   // aura::WindowObserver:
-  void OnWindowHierarchyChanging(const HierarchyChangeParams& params) override;
-  void OnWindowHierarchyChanged(const HierarchyChangeParams& params) override;
-  void OnWindowStackingChanged(aura::Window* window) override;
   void OnWindowPropertyChanged(aura::Window* window,
                                const void* key,
                                intptr_t old) override;
-  void OnWindowBoundsChanged(aura::Window* window,
-                             const gfx::Rect& old_bounds,
-                             const gfx::Rect& new_bounds) override;
-  void OnWindowDestroying(aura::Window* window) override;
-  void OnWindowDestroyed(aura::Window* window) override;
-  void OnWindowVisibilityChanging(aura::Window* window, bool visible) override;
-  void OnWindowVisibilityChanged(aura::Window* window, bool visible) override;
-  void OnWindowTitleChanged(aura::Window* window) override;
 
   // ::wm::TransientWindowObserver overrides:
   void OnTransientChildAdded(aura::Window* window,
@@ -399,8 +383,6 @@ class ASH_EXPORT WmWindow : public aura::WindowObserver,
 
   aura::Window* window_;
 
-  base::ObserverList<WmWindowObserver> observers_;
-
   bool added_transient_observer_ = false;
   base::ObserverList<WmTransientWindowObserver> transient_observers_;