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 40eb97c745918efc5318f416f04dd445e1ef3ba5..1a082ba3ebbea2bc55a138cd63f79c5aa356cb55 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&,
@@ -99,7 +104,8 @@ class PLATFORM_EXPORT ScrollableArea : public GarbageCollectedMixin,
   virtual LayoutRect ScrollIntoView(const LayoutRect& rect_in_content,
                                     const ScrollAlignment& align_x,
                                     const ScrollAlignment& align_y,
-                                    ScrollType = kProgrammaticScroll);
+                                    ScrollType = kProgrammaticScroll,
+                                    bool is_smooth = false);
 
   static bool ScrollBehaviorFromString(const String&, ScrollBehavior&);