Introduces a new scrollbar for message_center.

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 7719d8653ba25ef95eec94d92a06501f32de96b1..455c0023ce0634e8de8081cc82711fb840d7bf9d 100644
--- a/ui/views/controls/scrollbar/scroll_bar.cc
+++ b/ui/views/controls/scrollbar/scroll_bar.cc
@@ -31,6 +31,16 @@ int ScrollBar::GetMinPosition() const {
   return 0;
 }
 
+int ScrollBar::GetVisibleSize() const {
+  return GetLayoutSize();
+}
+
+void ScrollBar::OnMouseEnteredScrollView(const ui::MouseEvent& event) {
+}
+
+void ScrollBar::OnMouseExitedScrollView(const ui::MouseEvent& event) {
+}
+
 ScrollBar::ScrollBar(bool is_horiz)
     : is_horiz_(is_horiz),
       controller_(NULL),