Implement Element.scrollIntoView for scroll-behavior: smooth.

third_party/WebKit/Source/core/layout/LayoutObject.h

Index: third_party/WebKit/Source/core/layout/LayoutObject.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutObject.h b/third_party/WebKit/Source/core/layout/LayoutObject.h
index df829ee2b25d0b3e84a012f7ad843697e5f51369..815fdac1a8c6d90505de74a8c60dec1cbe791e1c 100644
--- a/third_party/WebKit/Source/core/layout/LayoutObject.h
+++ b/third_party/WebKit/Source/core/layout/LayoutObject.h
@@ -278,7 +278,8 @@ class CORE_EXPORT LayoutObject : public ImageResourceObserver,
       const ScrollAlignment& align_x = ScrollAlignment::kAlignCenterIfNeeded,
       const ScrollAlignment& align_y = ScrollAlignment::kAlignCenterIfNeeded,
       ScrollType = kProgrammaticScroll,
-      bool make_visible_in_visual_viewport = true);
+      bool make_visible_in_visual_viewport = true,
+      ScrollBehavior = kScrollBehaviorAuto);
 
   // Convenience function for getting to the nearest enclosing box of a
   // LayoutObject.