Update local BaseScrollBar::contents_scroll_offset_ on Update.

ui/views/controls/scrollbar/base_scroll_bar.cc

Index: ui/views/controls/scrollbar/base_scroll_bar.cc
diff --git a/ui/views/controls/scrollbar/base_scroll_bar.cc b/ui/views/controls/scrollbar/base_scroll_bar.cc
index 2e9d7f277562bfeab5132bbd39cb29e9e26b5922..99ec75a5510baa15918982b277ed4243e63e9ca2 100644
--- a/ui/views/controls/scrollbar/base_scroll_bar.cc
+++ b/ui/views/controls/scrollbar/base_scroll_bar.cc
@@ -388,7 +388,8 @@ void BaseScrollBar::ExecuteCommand(int id) {
 ///////////////////////////////////////////////////////////////////////////////
 // BaseScrollBar, ScrollBar implementation:
 
-void BaseScrollBar::Update(int viewport_size, int content_size,
+void BaseScrollBar::Update(int viewport_size,
+                           int content_size,
                            int contents_scroll_offset) {
   ScrollBar::Update(viewport_size, content_size, contents_scroll_offset);
 
@@ -404,6 +405,7 @@ void BaseScrollBar::Update(int viewport_size, int content_size,
     contents_scroll_offset = 0;
   if (contents_scroll_offset > content_size)
     contents_scroll_offset = content_size;
+  contents_scroll_offset_ = contents_scroll_offset;
 
   // Thumb Height and Thumb Pos.
   // The height of the thumb is the ratio of the Viewport height to the
@@ -498,7 +500,7 @@ int BaseScrollBar::CalculateThumbPosition(int contents_scroll_offset) const {
 }
 
 int BaseScrollBar::CalculateContentsOffset(int thumb_position,
-                                             bool scroll_to_middle) const {
+                                           bool scroll_to_middle) const {
   if (scroll_to_middle)
     thumb_position = thumb_position - (thumb_->GetSize() / 2);
   return (thumb_position * contents_size_) / GetTrackSize();