Introduces a new scrollbar for message_center.

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 3659c35c5db45f75e4a9b98a4ce11debcdaaa410..55211874f9381ebf227518ad3f2996fd0dad9d64 100644
--- a/ui/views/controls/scroll_view.cc
+++ b/ui/views/controls/scroll_view.cc
@@ -117,6 +117,8 @@ ScrollView::ScrollView()
       vert_sb_(new NativeScrollBar(false)),
       resize_corner_(NULL),
       hide_horizontal_scrollbar_(false) {
+  set_notify_enter_exit_on_child(true);
+
   AddChildView(contents_viewport_);
   AddChildView(header_viewport_);
 
@@ -252,15 +254,19 @@ void ScrollView::Layout() {
   }
 
   if (horiz_sb_required) {
+    int horiz_sb_visible_height = horiz_sb_->GetVisibleSize();
+    int height_offset = horiz_sb_visible_height - horiz_sb_height;
     horiz_sb_->SetBounds(0,
-                         viewport_bounds.bottom(),
+                         viewport_bounds.bottom() - height_offset,
                          viewport_bounds.right(),
-                         horiz_sb_height);
+                         horiz_sb_visible_height);
   }
   if (vert_sb_required) {
-    vert_sb_->SetBounds(viewport_bounds.right(),
+    int vert_sb_visible_width = vert_sb_->GetVisibleSize();
+    int width_offset = vert_sb_visible_width - vert_sb_width;
+    vert_sb_->SetBounds(viewport_bounds.right() - width_offset,
                         0,
-                        vert_sb_width,
+                        vert_sb_visible_width,
                         viewport_bounds.bottom());
   }
   if (resize_corner_required) {
@@ -312,6 +318,20 @@ 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::OnGestureEvent(ui::GestureEvent* event) {
   // If the event happened on one of the scrollbars, then those events are
   // sent directly to the scrollbars. Otherwise, only scroll events are sent to