Implement Element.scrollIntoView for scroll-behavior: smooth.

third_party/WebKit/Source/core/dom/Element.idl

Index: third_party/WebKit/Source/core/dom/Element.idl
diff --git a/third_party/WebKit/Source/core/dom/Element.idl b/third_party/WebKit/Source/core/dom/Element.idl
index 07e6d7aa90489f5b14954851fb6eb6dc062b6769..cc91237af8c92fd93d9bf6ef5410db99081ea774 100644
--- a/third_party/WebKit/Source/core/dom/Element.idl
+++ b/third_party/WebKit/Source/core/dom/Element.idl
@@ -94,7 +94,7 @@ interface Element : Node {
     ClientRectList getClientRects();
     ClientRect getBoundingClientRect();
     // FIXME: scrollIntoView() should have a ScrollIntoViewOptions dictionary argument.
-    void scrollIntoView(optional boolean alignWithTop);
+    [RaisesException] void scrollIntoView(optional (ScrollIntoViewOptions or boolean)? arg);
     [RuntimeEnabled=CSSOMSmoothScroll, ImplementedAs=scrollTo] void scroll(optional ScrollToOptions options);
     [RuntimeEnabled=CSSOMSmoothScroll, ImplementedAs=scrollTo] void scroll(unrestricted double x, unrestricted double y);
     [RuntimeEnabled=CSSOMSmoothScroll] void scrollTo(optional ScrollToOptions options);