Implement Element.scrollIntoView for scroll-behavior: smooth.

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

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
index fef30afdfad7a909217d58e949c98e9c91e8fca7..138d6f4f50ce3ac92759d1b80d71bda69355b57d 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -209,6 +209,13 @@ PlatformChromeClient* PaintLayerScrollableArea::GetChromeClient() const {
   return nullptr;
 }
 
+SmoothScrollSequencer* PaintLayerScrollableArea::GetSmoothScrollSequencer()
+    const {
+  if (Page* page = Box().GetFrame()->GetPage())
+    return page->GetSmoothScrollSequencer();
+  return nullptr;
+}
+
 GraphicsLayer* PaintLayerScrollableArea::LayerForScrolling() const {
   return Layer()->HasCompositedLayerMapping()
              ? Layer()->GetCompositedLayerMapping()->ScrollingContentsLayer()
@@ -1723,7 +1730,8 @@ LayoutRect PaintLayerScrollableArea::ScrollIntoView(
     const LayoutRect& rect,
     const ScrollAlignment& align_x,
     const ScrollAlignment& align_y,
-    ScrollType scroll_type) {
+    ScrollType scroll_type,
+    bool is_smooth) {
   LayoutRect local_expose_rect(
       Box()
           .AbsoluteToLocalQuad(FloatQuad(FloatRect(rect)), kUseTransforms)
@@ -1736,8 +1744,14 @@ LayoutRect PaintLayerScrollableArea::ScrollIntoView(
   ScrollOffset old_scroll_offset = GetScrollOffset();
   ScrollOffset new_scroll_offset(ClampScrollOffset(RoundedIntSize(
       ToScrollOffset(FloatPoint(r.Location()) + old_scroll_offset))));
-  SetScrollOffset(new_scroll_offset, scroll_type, kScrollBehaviorInstant);
-  ScrollOffset scroll_offset_difference = GetScrollOffset() - old_scroll_offset;
+  if (is_smooth) {
+    DCHECK(scroll_type != kUserScroll);
+    GetSmoothScrollSequencer()->QueueAnimation(this, new_scroll_offset);
+  } else {
+    SetScrollOffset(new_scroll_offset, scroll_type, kScrollBehaviorInstant);
+  }
+  ScrollOffset scroll_offset_difference =
+      ClampScrollOffset(new_scroll_offset) - old_scroll_offset;
   local_expose_rect.Move(-LayoutSize(scroll_offset_difference));
 
   LayoutRect intersect =