mash shelf: Don't create shelf DimmerView in ShelfWidget on mus

ash/common/shelf/wm_dimmer_view.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_COMMON_SHELF_WM_DIMMER_VIEW_H_
+#define ASH_COMMON_SHELF_WM_DIMMER_VIEW_H_
+
+namespace views {
+class Widget;
+}
+
+namespace ash {
+
+// An interface around a widget and view that dim shelf items slightly when a
+// window is maximized and visible. See DimmerView for details. This interface
+// exists to avoid dependencies between ash common shelf code and the aura-only
+// implementation of DimmerView.
+// TODO(jamescook): Delete this after material design ships, as MD will not
+// require shelf dimming. http://crbug.com/614453
+class WmDimmerView {
+ public:
+  // Returns the widget that holds the dimmer view.
+  virtual views::Widget* GetDimmerWidget() = 0;
+
+  // Force the dimmer to be undimmed (e.g. by an open context menu).
+  virtual void ForceUndimming(bool force) = 0;
+
+  // Returns the current alpha used by the dimming bar.
+  virtual int GetDimmingAlphaForTest() = 0;
+
+ protected:
+  virtual ~WmDimmerView() {}
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_SHELF_WM_DIMMER_VIEW_H_