MacViews: Reveal scrollbars when resting on the trackpad.

ui/views/controls/scrollbar/scroll_bar.cc

Index: ui/views/controls/scrollbar/scroll_bar.cc
diff --git a/ui/views/controls/scrollbar/scroll_bar.cc b/ui/views/controls/scrollbar/scroll_bar.cc
index bfe75dca835edd476890b3fe33b0390ad91902e9..a003aa1d2a0a9c77e37e5e2786f8f8766e2b3499 100644
--- a/ui/views/controls/scrollbar/scroll_bar.cc
+++ b/ui/views/controls/scrollbar/scroll_bar.cc
@@ -35,11 +35,9 @@ int ScrollBar::GetContentOverlapSize() const {
   return 0;
 }
 
-void ScrollBar::OnMouseEnteredScrollView(const ui::MouseEvent& event) {
-}
-
-void ScrollBar::OnMouseExitedScrollView(const ui::MouseEvent& event) {
-}
+void ScrollBar::OnMouseEnteredScrollView(const ui::MouseEvent& event) {}
+void ScrollBar::OnMouseExitedScrollView(const ui::MouseEvent& event) {}
+void ScrollBar::ObserveScrollEvent(const ui::ScrollEvent& event) {}
 
 ScrollBar::ScrollBar(bool is_horiz)
     : is_horiz_(is_horiz),