Ash: Fix WM window resize shadow stacking.

ash/wm/resize_shadow.h

Index: ash/wm/resize_shadow.h
diff --git a/ash/wm/resize_shadow.h b/ash/wm/resize_shadow.h
index d9003abafc74c4378b678384032e44ba8909e5ea..3ebcf46c798a7ad114a3be3357eb84f7010f791b 100644
--- a/ash/wm/resize_shadow.h
+++ b/ash/wm/resize_shadow.h
@@ -32,6 +32,7 @@ class ResizeShadow : public aura::WindowObserver {
                              const gfx::Rect& old_bounds,
                              const gfx::Rect& new_bounds) override;
   void OnWindowHierarchyChanged(const HierarchyChangeParams& params) override;
+  void OnWindowStackingChanged(aura::Window* window) override;
 
   // Shows resize effects for one or more edges based on a |hit_test| code, such
   // as HTRIGHT or HTBOTTOMRIGHT.