[not for review - epic CL] Adding Elastic+Momentum+Layered scrolling to views::ScrollView

ui/views/controls/scrollbar/cocoa_scroll_bar.h

Index: ui/views/controls/scrollbar/cocoa_scroll_bar.h
diff --git a/ui/views/controls/scrollbar/cocoa_scroll_bar.h b/ui/views/controls/scrollbar/cocoa_scroll_bar.h
index 2cca52a6e380aa0400baf2b0c70ec5152762b9eb..35043a1398612ba6276d64991696b18e6937d281 100644
--- a/ui/views/controls/scrollbar/cocoa_scroll_bar.h
+++ b/ui/views/controls/scrollbar/cocoa_scroll_bar.h
@@ -26,8 +26,10 @@ class VIEWS_EXPORT CocoaScrollBar : public BaseScrollBar,
   explicit CocoaScrollBar(bool horizontal);
   ~CocoaScrollBar() override;
 
-  // BaseScrollBar:
-  void ScrollToPosition(int position) override;
+  // ScrollBar:
+  void Update(int viewport_size,
+              int content_size,
+              int contents_scroll_offset) override;
 
   // ViewsScrollbarBridgeDelegate:
   void OnScrollerStyleChanged() override;
@@ -100,6 +102,9 @@ class VIEWS_EXPORT CocoaScrollBar : public BaseScrollBar,
   // the scrollbar as the hiding animation.
   gfx::SlideAnimation thickness_animation_;
 
+  // The scroll offset from the last adjustment to the scroll bar.
+  int last_contents_scroll_offset_;
+
   // True when the scrollbar is expanded.
   bool is_expanded_;