Replace WmWindowObserver with aura::WindowObserver.

ash/common/wm/overview/window_grid.h

Index: ash/common/wm/overview/window_grid.h
diff --git a/ash/common/wm/overview/window_grid.h b/ash/common/wm/overview/window_grid.h
index a18f6a60d3984958a444aafde069e16f0702f470..67f4f567a117e390af09df0f17674d82214ea7d2 100644
--- a/ash/common/wm/overview/window_grid.h
+++ b/ash/common/wm/overview/window_grid.h
@@ -13,9 +13,9 @@
 
 #include "ash/common/wm/overview/window_selector.h"
 #include "ash/common/wm/window_state_observer.h"
-#include "ash/common/wm_window_observer.h"
 #include "base/macros.h"
 #include "base/scoped_observer.h"
+#include "ui/aura/window_observer.h"
 
 namespace views {
 class Widget;
@@ -47,7 +47,7 @@ class WindowSelectorItem;
 //    0, 1, 2, 3, 4, 5, 6
 // The selector is switched to the next window grid (if available) or wrapped if
 // it reaches the end of its movement sequence.
-class ASH_EXPORT WindowGrid : public WmWindowObserver,
+class ASH_EXPORT WindowGrid : public aura::WindowObserver,
                               public wm::WindowStateObserver {
  public:
   WindowGrid(WmWindow* root_window,
@@ -115,10 +115,10 @@ class ASH_EXPORT WindowGrid : public WmWindowObserver,
     return window_list_;
   }
 
-  // WmWindowObserver:
-  void OnWindowDestroying(WmWindow* window) override;
+  // aura::WindowObserver:
+  void OnWindowDestroying(aura::Window* window) override;
   // TODO(flackr): Handle window bounds changed in WindowSelectorItem.
-  void OnWindowBoundsChanged(WmWindow* window,
+  void OnWindowBoundsChanged(aura::Window* window,
                              const gfx::Rect& old_bounds,
                              const gfx::Rect& new_bounds) override;
 
@@ -169,7 +169,7 @@ class ASH_EXPORT WindowGrid : public WmWindowObserver,
   // Vector containing all the windows in this grid.
   std::vector<std::unique_ptr<WindowSelectorItem>> window_list_;
 
-  ScopedObserver<WmWindow, WindowGrid> window_observer_;
+  ScopedObserver<aura::Window, WindowGrid> window_observer_;
   ScopedObserver<wm::WindowState, WindowGrid> window_state_observer_;
 
   // Widget that darkens the screen background.