Replace WmWindowObserver with aura::WindowObserver.

ash/common/wm/overview/window_selector.h

Index: ash/common/wm/overview/window_selector.h
diff --git a/ash/common/wm/overview/window_selector.h b/ash/common/wm/overview/window_selector.h
index 5512f4d89e89d595cabd0ec98c9bbea8c8451575..a5cb74386e85c081ecb2aa3dd8cc009bc8a9c381 100644
--- a/ash/common/wm/overview/window_selector.h
+++ b/ash/common/wm/overview/window_selector.h
@@ -14,9 +14,9 @@
 
 #include "ash/ash_export.h"
 #include "ash/common/wm_activation_observer.h"
-#include "ash/common/wm_window_observer.h"
 #include "base/macros.h"
 #include "base/time/time.h"
+#include "ui/aura/window_observer.h"
 #include "ui/display/display_observer.h"
 #include "ui/gfx/image/image_skia.h"
 #include "ui/views/controls/textfield/textfield_controller.h"
@@ -35,7 +35,7 @@ class WindowGrid;
 // The WindowSelector shows a grid of all of your windows, allowing to select
 // one by clicking or tapping on it.
 class ASH_EXPORT WindowSelector : public display::DisplayObserver,
-                                  public WmWindowObserver,
+                                  public aura::WindowObserver,
                                   public WmActivationObserver,
                                   public views::TextfieldController {
  public:
@@ -91,10 +91,9 @@ class ASH_EXPORT WindowSelector : public display::DisplayObserver,
   void OnDisplayMetricsChanged(const display::Display& display,
                                uint32_t metrics) override;
 
-  // WmWindowObserver:
-  void OnWindowTreeChanged(WmWindow* window,
-                           const TreeChangeParams& params) override;
-  void OnWindowDestroying(WmWindow* window) override;
+  // aura::WindowObserver:
+  void OnWindowHierarchyChanged(const HierarchyChangeParams& params) override;
+  void OnWindowDestroying(aura::Window* window) override;
 
   // WmActivationObserver
   void OnWindowActivated(WmWindow* gained_active,