Implement CSSOM Smooth Scroll API

Source/core/frame/DOMWindow.cpp

Index: Source/core/frame/DOMWindow.cpp
diff --git a/Source/core/frame/DOMWindow.cpp b/Source/core/frame/DOMWindow.cpp
index 28661b8e793fe0cf85b0d9e0df6f8988365e1dd5..c44cfc897726df81efef35d8ee0fb676ef9c5a5a 100644
--- a/Source/core/frame/DOMWindow.cpp
+++ b/Source/core/frame/DOMWindow.cpp
@@ -1416,8 +1416,7 @@ void DOMWindow::scrollBy(int x, int y, const Dictionary& scrollOptions, Exceptio
         return;
 
     IntSize scaledOffset(x * m_frame->pageZoomFactor(), y * m_frame->pageZoomFactor());
-    // FIXME: Use scrollBehavior to decide whether to scroll smoothly or instantly.
-    view->scrollBy(scaledOffset);
+    view->scrollBy(scaledOffset, scrollBehavior);
 }
 
 void DOMWindow::scrollTo(int x, int y, const Dictionary& scrollOptions, ExceptionState& exceptionState) const
@@ -1436,8 +1435,7 @@ void DOMWindow::scrollTo(int x, int y, const Dictionary& scrollOptions, Exceptio
         return;
 
     IntPoint layoutPos(x * m_frame->pageZoomFactor(), y * m_frame->pageZoomFactor());
-    // FIXME: Use scrollBehavior to decide whether to scroll smoothly or instantly.
-    view->setScrollPosition(layoutPos);
+    view->setScrollPosition(layoutPos, scrollBehavior);
 }
 
 void DOMWindow::moveBy(float x, float y) const