Refactors WindowResizers to use ash/wm/common

ash/wm/common/shelf/wm_shelf_observer.h

Index: ash/wm/common/shelf/wm_shelf_observer.h
diff --git a/ash/wm/common/shelf/wm_shelf_observer.h b/ash/wm/common/shelf/wm_shelf_observer.h
index 44d82773990d5983186460aa6ec1d4eb4454a955..299e6b84d9236739a3c0d6b4b5abcf97dee0a59e 100644
--- a/ash/wm/common/shelf/wm_shelf_observer.h
+++ b/ash/wm/common/shelf/wm_shelf_observer.h
@@ -6,7 +6,6 @@
 #define ASH_WM_COMMON_SHELF_WM_SHELF_OBSERVER_H_
 
 #include "ash/ash_export.h"
-// TODO(sky): refactor into common.
 #include "ash/wm/common/background_animator.h"
 #include "ash/wm/common/shelf/wm_shelf_types.h"
 
@@ -20,6 +19,8 @@ class ASH_EXPORT WmShelfObserver {
  public:
   virtual void OnBackgroundUpdated(ShelfBackgroundType background_type,
                                    BackgroundAnimatorChangeType change_type) {}
+  virtual void WillChangeVisibilityState(ShelfVisibilityState new_state) {}
+  virtual void OnShelfIconPositionsChanged() {}
 
  protected:
   virtual ~WmShelfObserver() {}