Refactors DockedWindowLayoutManager in terms of ash/wm/common

ash/wm/common/shelf/wm_shelf_observer.h

+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ASH_WM_COMMON_SHELF_WM_SHELF_OBSERVER_H_
+#define ASH_WM_COMMON_SHELF_WM_SHELF_OBSERVER_H_
+
+#include "ash/ash_export.h"
+// TODO(sky): refactor into common.
+#include "ash/shelf/background_animator.h"
+#include "ash/wm/common/shelf/wm_shelf_types.h"
+
+namespace ash {
+namespace wm {
+
+class WmWindow;
+
+// Used to observe changes to the shelf.
+class ASH_EXPORT WmShelfObserver {
+ public:
+  virtual void OnBackgroundUpdated(ShelfBackgroundType background_type,
+                                   BackgroundAnimatorChangeType change_type) {}
+
+ protected:
+  virtual ~WmShelfObserver() {}
+};
+
+}  // namespace wm
+}  // namespace ash
+
+#endif  // ASH_WM_COMMON_SHELF_WM_SHELF_OBSERVER_H_