Implement Element.scrollIntoView for scroll-behavior: smooth.

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

Index: third_party/WebKit/Source/core/frame/RootFrameViewport.h
diff --git a/third_party/WebKit/Source/core/frame/RootFrameViewport.h b/third_party/WebKit/Source/core/frame/RootFrameViewport.h
index 72c87ed639f7c4c2d864304f34e3728d05ff1892..cbec0f0ab3e7afac016571959fe26eda0f99cfb9 100644
--- a/third_party/WebKit/Source/core/frame/RootFrameViewport.h
+++ b/third_party/WebKit/Source/core/frame/RootFrameViewport.h
@@ -60,7 +60,8 @@ class CORE_EXPORT RootFrameViewport final
   LayoutRect scrollIntoView(const LayoutRect& rectInContent,
                             const ScrollAlignment& alignX,
                             const ScrollAlignment& alignY,
-                            ScrollType = ProgrammaticScroll) override;
+                            ScrollType = ProgrammaticScroll,
+                            bool isSmooth = false) override;
   IntRect visibleContentRect(
       IncludeScrollbarsInRect = ExcludeScrollbars) const override;
   bool shouldUseIntegerScrollOffset() const override;
@@ -94,6 +95,7 @@ class CORE_EXPORT RootFrameViewport final
   ScrollResult userScroll(ScrollGranularity, const FloatSize&) override;
   bool scrollAnimatorEnabled() const override;
   HostWindow* getHostWindow() const override;
+  SmoothScrollSequencer* getSmoothScrollSequencer() const override;
   void serviceScrollAnimations(double) override;
   void updateCompositorScrollAnimations() override;
   void cancelProgrammaticScrollAnimation() override;