Use overlay scrollbars for the cros system menu.

ui/views/controls/scrollbar/overlay_scroll_bar.cc

 // 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.
 
 #include "ui/views/controls/scrollbar/overlay_scroll_bar.h"
 
 #include "base/macros.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/core/SkXfermode.h"
 #include "ui/gfx/canvas.h"
@@ skipping 121 matching lines @@
     case ui::ET_SCROLL_FLING_START:
     case ui::ET_GESTURE_END:
       animation_.Hide();
       break;
     default:
       break;
   }
   BaseScrollBar::OnGestureEvent(event);
 }
 
-gfx::Size OverlayScrollBar::GetPreferredSize() const {
-  return gfx::Size();
-}
-
 void OverlayScrollBar::Layout() {
   gfx::Rect thumb_bounds = GetTrackBounds();
   BaseScrollBarThumb* thumb = GetThumb();
   if (IsHorizontal()) {
     thumb_bounds.set_x(thumb->x());
     thumb_bounds.set_width(thumb->width());
   } else {
     thumb_bounds.set_y(thumb->y());
     thumb_bounds.set_height(thumb->height());
   }
   thumb->SetBoundsRect(thumb_bounds);
 }
 
-void OverlayScrollBar::OnPaint(gfx::Canvas* canvas) {
-}
-
 }  // namespace views