Implement Element.scrollIntoView for scroll-behavior: smooth.

third_party/WebKit/Source/core/frame/RootFrameViewport.cpp

Index: third_party/WebKit/Source/core/frame/RootFrameViewport.cpp
diff --git a/third_party/WebKit/Source/core/frame/RootFrameViewport.cpp b/third_party/WebKit/Source/core/frame/RootFrameViewport.cpp
index 1f4632132bb43eaf0d7c679da4023ffbf3a4fed0..516383333a5c0ca6237df85b3a19bc0f42834766 100644
--- a/third_party/WebKit/Source/core/frame/RootFrameViewport.cpp
+++ b/third_party/WebKit/Source/core/frame/RootFrameViewport.cpp
@@ -209,7 +209,8 @@ ScrollBehavior RootFrameViewport::scrollBehaviorStyle() const {
 LayoutRect RootFrameViewport::scrollIntoView(const LayoutRect& rectInContent,
                                              const ScrollAlignment& alignX,
                                              const ScrollAlignment& alignY,
-                                             ScrollType scrollType) {
+                                             ScrollType scrollType,
+                                             bool isSmooth) {
   // We want to move the rect into the viewport that excludes the scrollbars so
   // we intersect the visual viewport with the scrollbar-excluded frameView
   // content rect. However, we don't use visibleContentRect directly since it
@@ -229,8 +230,14 @@ LayoutRect RootFrameViewport::scrollIntoView(const LayoutRect& rectInContent,
   LayoutRect targetViewport = ScrollAlignment::getRectToExpose(
       viewRectInContent, rectInContent, alignX, alignY);
   if (targetViewport != viewRectInContent) {
-    setScrollOffset(ScrollOffset(targetViewport.x(), targetViewport.y()),
-                    scrollType);
+    if (isSmooth) {
+      DCHECK(scrollType != UserScroll);
+      getProgrammaticScrollCoordinator()->queueAnimation(
+          this, ScrollOffset(targetViewport.x(), targetViewport.y()));
+    } else {
+      setScrollOffset(ScrollOffset(targetViewport.x(), targetViewport.y()),
+                      scrollType);
+    }
   }
 
   // RootFrameViewport only changes the viewport relative to the document so we
@@ -430,6 +437,11 @@ HostWindow* RootFrameViewport::getHostWindow() const {
   return layoutViewport().getHostWindow();
 }
 
+ProgrammaticScrollCoordinator*
+RootFrameViewport::getProgrammaticScrollCoordinator() const {
+  return layoutViewport().getProgrammaticScrollCoordinator();
+}
+
 void RootFrameViewport::serviceScrollAnimations(double monotonicTime) {
   ScrollableArea::serviceScrollAnimations(monotonicTime);
   layoutViewport().serviceScrollAnimations(monotonicTime);