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 88564c1998ba2953560f23f7d4a073a71ebab6db..39c9316ce0b7f34a9fd7f9445abd0e6cfa0caebd 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -209,6 +209,13 @@ HostWindow* PaintLayerScrollableArea::getHostWindow() const {
   return nullptr;
 }
 
+SmoothScrollSequencer* PaintLayerScrollableArea::getSmoothScrollSequencer()
+    const {
+  if (Page* page = box().frame()->page())
+    return page->smoothScrollSequencer();
+  return nullptr;
+}
+
 GraphicsLayer* PaintLayerScrollableArea::layerForScrolling() const {
   return layer()->hasCompositedLayerMapping()
              ? layer()->compositedLayerMapping()->scrollingContentsLayer()
@@ -1670,7 +1677,8 @@ LayoutRect PaintLayerScrollableArea::scrollIntoView(
     const LayoutRect& rect,
     const ScrollAlignment& alignX,
     const ScrollAlignment& alignY,
-    ScrollType scrollType) {
+    ScrollType scrollType,
+    bool isSmooth) {
   LayoutRect localExposeRect(
       box()
           .absoluteToLocalQuad(FloatQuad(FloatRect(rect)), UseTransforms)
@@ -1684,7 +1692,12 @@ LayoutRect PaintLayerScrollableArea::scrollIntoView(
   ScrollOffset oldScrollOffset = getScrollOffset();
   ScrollOffset newScrollOffset(clampScrollOffset(roundedIntSize(
       toScrollOffset(FloatPoint(r.location()) + oldScrollOffset))));
-  setScrollOffset(newScrollOffset, scrollType, ScrollBehaviorInstant);
+  if (isSmooth) {
+    DCHECK(scrollType != UserScroll);
+    getSmoothScrollSequencer()->queueAnimation(this, newScrollOffset);
+  } else {
+    setScrollOffset(newScrollOffset, scrollType, ScrollBehaviorInstant);
+  }
   ScrollOffset scrollOffsetDifference = getScrollOffset() - oldScrollOffset;
   localExposeRect.move(-LayoutSize(scrollOffsetDifference));