Refactors DockedWindowLayoutManager in terms of ash/wm/common

ash/wm/common/shelf/wm_shelf.h

Index: ash/wm/common/shelf/wm_shelf.h
diff --git a/ash/wm/common/shelf/wm_shelf.h b/ash/wm/common/shelf/wm_shelf.h
new file mode 100644
index 0000000000000000000000000000000000000000..2bcac6e1af0bac3d3ef0a8ada0965e3b669a053f
--- /dev/null
+++ b/ash/wm/common/shelf/wm_shelf.h
@@ -0,0 +1,39 @@
+// 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_H_
+#define ASH_WM_COMMON_SHELF_WM_SHELF_H_
+
+#include "ash/ash_export.h"
+#include "ash/wm/common/shelf/wm_shelf_types.h"
+
+namespace ash {
+namespace wm {
+
+class WmShelfObserver;
+class WmWindow;
+
+// Used for accessing global state.
+class ASH_EXPORT WmShelf {
+ public:
+  // Returns the window showing the shelf.
+  virtual WmWindow* GetWindow() = 0;
+
+  virtual ShelfAlignment GetAlignment() = 0;
+
+  virtual ShelfBackgroundType GetBackgroundType() = 0;
+
+  virtual void UpdateVisibilityState() = 0;
+
+  virtual void AddObserver(WmShelfObserver* observer) = 0;
+  virtual void RemoveObserver(WmShelfObserver* observer) = 0;
+
+ protected:
+  virtual ~WmShelf() {}
+};
+
+}  // namespace wm
+}  // namespace ash
+
+#endif  // ASH_WM_COMMON_SHELF_WM_SHELF_H_