Use overlay scrollbars for the cros system menu.

ui/views/controls/scrollbar/overlay_scroll_bar.h

 // Copyright 2013 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 UI_VIEWS_CONTROLS_SCROLLBAR_OVERLAY_SCROLL_BAR_H_
 #define UI_VIEWS_CONTROLS_SCROLLBAR_OVERLAY_SCROLL_BAR_H_
 
 #include "base/macros.h"
 #include "ui/gfx/animation/slide_animation.h"
 #include "ui/views/controls/scrollbar/base_scroll_bar.h"
@@ skipping 11 matching lines @@
   gfx::Rect GetTrackBounds() const override;
   void OnGestureEvent(ui::GestureEvent* event) override;
 
   // ScrollBar overrides:
   int GetLayoutSize() const override;
   int GetContentOverlapSize() const override;
   void OnMouseEnteredScrollView(const ui::MouseEvent& event) override;
   void OnMouseExitedScrollView(const ui::MouseEvent& event) override;
 
   // View overrides:
-  gfx::Size GetPreferredSize() const override;
   void Layout() override;
-  void OnPaint(gfx::Canvas* canvas) override;
 
  private:
   gfx::SlideAnimation animation_;
   DISALLOW_COPY_AND_ASSIGN(OverlayScrollBar);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_CONTROLS_SCROLLBAR_OVERLAY_SCROLL_BAR_H_