Use overlay scrollbars for the cros system menu.

ui/views/controls/scrollbar/overlay_scroll_bar.cc

Index: ui/views/controls/scrollbar/overlay_scroll_bar.cc
diff --git a/ui/views/controls/scrollbar/overlay_scroll_bar.cc b/ui/views/controls/scrollbar/overlay_scroll_bar.cc
index 8da5f7d4290e92a8d0753b53c320a96993afdc4f..4a5e27e1b632763a6cf88f304595148f5ce541c1 100644
--- a/ui/views/controls/scrollbar/overlay_scroll_bar.cc
+++ b/ui/views/controls/scrollbar/overlay_scroll_bar.cc
@@ -139,10 +139,6 @@ void OverlayScrollBar::OnGestureEvent(ui::GestureEvent* event) {
   BaseScrollBar::OnGestureEvent(event);
 }
 
-gfx::Size OverlayScrollBar::GetPreferredSize() const {
-  return gfx::Size();
-}
-
 void OverlayScrollBar::Layout() {
   gfx::Rect thumb_bounds = GetTrackBounds();
   BaseScrollBarThumb* thumb = GetThumb();
@@ -156,7 +152,4 @@ void OverlayScrollBar::Layout() {
   thumb->SetBoundsRect(thumb_bounds);
 }
 
-void OverlayScrollBar::OnPaint(gfx::Canvas* canvas) {
-}
-
 }  // namespace views