Implement Element.scrollIntoView for scroll-behavior: smooth.

third_party/WebKit/Source/platform/scroll/ScrollableArea.h

Index: third_party/WebKit/Source/platform/scroll/ScrollableArea.h
diff --git a/third_party/WebKit/Source/platform/scroll/ScrollableArea.h b/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
index e3cd362d3aade216dffba643c8edd71448b780fa..0f626eef3074b24572311f13d7ae3f0f849b7cd0 100644
--- a/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
+++ b/third_party/WebKit/Source/platform/scroll/ScrollableArea.h
@@ -53,6 +53,7 @@ class ProgrammaticScrollAnimator;
 struct ScrollAlignment;
 class ScrollAnchor;
 class ScrollAnimatorBase;
+class SmoothScrollSequencer;
 class CompositorAnimationTimeline;
 
 enum IncludeScrollbarsInRect {
@@ -77,6 +78,10 @@ class PLATFORM_EXPORT ScrollableArea : public GarbageCollectedMixin,
 
   virtual PlatformChromeClient* GetChromeClient() const { return 0; }
 
+  virtual SmoothScrollSequencer* GetSmoothScrollSequencer() const {
+    return nullptr;
+  }
+
   virtual ScrollResult UserScroll(ScrollGranularity, const ScrollOffset&);
 
   virtual void SetScrollOffset(const ScrollOffset&,
@@ -99,6 +104,7 @@ class PLATFORM_EXPORT ScrollableArea : public GarbageCollectedMixin,
   virtual LayoutRect ScrollIntoView(const LayoutRect& rect_in_content,
                                     const ScrollAlignment& align_x,
                                     const ScrollAlignment& align_y,
+                                    bool is_smooth,
                                     ScrollType = kProgrammaticScroll);
 
   static bool ScrollBehaviorFromString(const String&, ScrollBehavior&);
@@ -412,7 +418,7 @@ class PLATFORM_EXPORT ScrollableArea : public GarbageCollectedMixin,
   virtual void ScrollbarVisibilityChanged() {}
 
  private:
-  void ProgrammaticScrollHelper(const ScrollOffset&, ScrollBehavior);
+  void ProgrammaticScrollHelper(const ScrollOffset&, ScrollBehavior, bool);
   void UserScrollHelper(const ScrollOffset&, ScrollBehavior);
 
   void FadeOverlayScrollbarsTimerFired(TimerBase*);