Implement Element.scrollIntoView for scroll-behavior: smooth.

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 572 matching lines @@
 
   void scrollToPosition(const FloatPoint&,
                         ScrollBehavior = ScrollBehaviorInstant);
   void scrollByRecursively(const ScrollOffset& delta);
   // If makeVisibleInVisualViewport is set, the visual viewport will be scrolled
   // if required to make the rect visible.
   void scrollRectToVisible(const LayoutRect&,
                            const ScrollAlignment& alignX,
                            const ScrollAlignment& alignY,
                            ScrollType = ProgrammaticScroll,
-                           bool makeVisibleInVisualViewport = true);
+                           bool makeVisibleInVisualViewport = true,
+                           ScrollBehavior = ScrollBehaviorAuto);
 
   LayoutRectOutsets marginBoxOutsets() const override {
     return m_marginBoxOutsets;
   }
   LayoutUnit marginTop() const override { return m_marginBoxOutsets.top(); }
   LayoutUnit marginBottom() const override {
     return m_marginBoxOutsets.bottom();
   }
   LayoutUnit marginLeft() const override { return m_marginBoxOutsets.left(); }
   LayoutUnit marginRight() const override { return m_marginBoxOutsets.right(); }
@@ skipping 1098 matching lines @@
          breakValue == EBreakBetween::kLeft ||
          breakValue == EBreakBetween::kPage ||
          breakValue == EBreakBetween::kRecto ||
          breakValue == EBreakBetween::kRight ||
          breakValue == EBreakBetween::kVerso;
 }
 
 }  // namespace blink
 
 #endif  // LayoutBox_h