Implement Element.scrollIntoView for scroll-behavior: smooth.

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
index c9683ae60dde99f05576f779e594b990bad25c79..dc4ef2492deaf36e03b210372188031c686363e9 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
@@ -240,6 +240,8 @@ class CORE_EXPORT PaintLayerScrollableArea final
 
   PlatformChromeClient* GetChromeClient() const override;
 
+  SmoothScrollSequencer* GetSmoothScrollSequencer() const override;
+
   // For composited scrolling, we allocate an extra GraphicsLayer to hold
   // onto the scrolling content. The layer can be shifted on the GPU and
   // composited at little cost.
@@ -391,7 +393,8 @@ class CORE_EXPORT PaintLayerScrollableArea final
   LayoutRect ScrollIntoView(const LayoutRect&,
                             const ScrollAlignment& align_x,
                             const ScrollAlignment& align_y,
-                            ScrollType = kProgrammaticScroll) override;
+                            ScrollType = kProgrammaticScroll,
+                            bool is_smooth = false) override;
 
   // Returns true if scrollable area is in the FrameView's collection of
   // scrollable areas. This can only happen if we're scrollable, visible to hit