Refactors DockedWindowLayoutManager in terms of 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
new file mode 100644
index 0000000000000000000000000000000000000000..4aa1b4b30f8687373b1bf354ca96e00aac9825ff
--- /dev/null
+++ b/ash/wm/common/shelf/wm_shelf_observer.h
@@ -0,0 +1,31 @@
+// 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_