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 98c634e298f3e9b6b6d2a31cc326aaeefac8c51c..d4dba5b1fea1d328c96c274c13c3197a6354d16e 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -210,6 +210,13 @@ HostWindow* PaintLayerScrollableArea::getHostWindow() const {
   return nullptr;
 }
 
+ProgrammaticScrollCoordinator*
+PaintLayerScrollableArea::getProgrammaticScrollCoordinator() const {
+  if (Page* page = box().frame()->page())
+    return page->scrollingCoordinator()->programmaticScrollCoordinator();
+  return nullptr;
+}
+
 GraphicsLayer* PaintLayerScrollableArea::layerForScrolling() const {
   return layer()->hasCompositedLayerMapping()
              ? layer()->compositedLayerMapping()->scrollingContentsLayer()
@@ -1634,7 +1641,8 @@ 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)
@@ -1648,7 +1656,12 @@ LayoutRect PaintLayerScrollableArea::scrollIntoView(
   ScrollOffset oldScrollOffset = getScrollOffset();
   ScrollOffset newScrollOffset(clampScrollOffset(roundedIntSize(
       toScrollOffset(FloatPoint(r.location()) + oldScrollOffset))));
-  setScrollOffset(newScrollOffset, scrollType, ScrollBehaviorInstant);
+  if (isSmooth) {
+    DCHECK(scrollType != UserScroll);
+    getProgrammaticScrollCoordinator()->queueAnimation(this, newScrollOffset);
+  } else {
+    setScrollOffset(newScrollOffset, scrollType, ScrollBehaviorInstant);
+  }
   ScrollOffset scrollOffsetDifference = getScrollOffset() - oldScrollOffset;
   localExposeRect.move(-LayoutSize(scrollOffsetDifference));