Implement Element.scrollIntoView for scroll-behavior: smooth.

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

Index: third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.h
diff --git a/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.h b/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.h
index f8a365c32b9584f2e5efabc5ac292e62cd27e0b4..8f1240fa127a5939d3dde87a419d3a1437a9c4f6 100644
--- a/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.h
+++ b/third_party/WebKit/Source/platform/scroll/ProgrammaticScrollAnimator.h
@@ -30,7 +30,8 @@ class ProgrammaticScrollAnimator : public ScrollAnimatorCompositorCoordinator {
   virtual ~ProgrammaticScrollAnimator();
 
   void ScrollToOffsetWithoutAnimation(const ScrollOffset&);
-  void AnimateToOffset(const ScrollOffset&);
+  void AnimateToOffset(const ScrollOffset&,
+                       bool sequenced_for_smooth_scroll = false);
 
   // ScrollAnimatorCompositorCoordinator implementation.
   void ResetAnimationState() override;
@@ -52,11 +53,13 @@ class ProgrammaticScrollAnimator : public ScrollAnimatorCompositorCoordinator {
   explicit ProgrammaticScrollAnimator(ScrollableArea*);
 
   void NotifyOffsetChanged(const ScrollOffset&);
+  void AnimationFinished();
 
   Member<ScrollableArea> scrollable_area_;
   std::unique_ptr<CompositorScrollOffsetAnimationCurve> animation_curve_;
   ScrollOffset target_offset_;
   double start_time_;
+  bool sequenced_for_smooth_scroll_;
 };
 
 }  // namespace blink