Implement Sebastien's overlay scrollbars for native UI (Views).

ui/views/controls/scroll_view.cc

Index: ui/views/controls/scroll_view.cc
diff --git a/ui/views/controls/scroll_view.cc b/ui/views/controls/scroll_view.cc
index b62972d894f5f99ea6e2fd30ba37486025bf7bb6..77c12b62bb4d38433baa99085a54002a3dc2e1b0 100644
--- a/ui/views/controls/scroll_view.cc
+++ b/ui/views/controls/scroll_view.cc
@@ -456,20 +456,6 @@ bool ScrollView::OnMouseWheel(const ui::MouseWheelEvent& e) {
   return processed;
 }
 
-void ScrollView::OnMouseEntered(const ui::MouseEvent& event) {
-  if (horiz_sb_)
-    horiz_sb_->OnMouseEnteredScrollView(event);
-  if (vert_sb_)
-    vert_sb_->OnMouseEnteredScrollView(event);
-}
-
-void ScrollView::OnMouseExited(const ui::MouseEvent& event) {
-  if (horiz_sb_)
-    horiz_sb_->OnMouseExitedScrollView(event);
-  if (vert_sb_)
-    vert_sb_->OnMouseExitedScrollView(event);
-}
-
 void ScrollView::OnScrollEvent(ui::ScrollEvent* event) {
 #if defined(OS_MACOSX)
   // TODO(tapted): Send |event| to a cc::InputHandler. For now, there's nothing