Add WebView API for smoothScroll

Source/web/WebViewImpl.cpp

Index: Source/web/WebViewImpl.cpp
diff --git a/Source/web/WebViewImpl.cpp b/Source/web/WebViewImpl.cpp
index ee14f410867c89d3d9746bcbf60ede4690418e14..0c863d8e2b06fd81cbf09ad1d4d8651b5b1d4bda 100644
--- a/Source/web/WebViewImpl.cpp
+++ b/Source/web/WebViewImpl.cpp
@@ -2874,6 +2874,12 @@ bool WebViewImpl::scrollFocusedNodeIntoRect(const WebRect& rectInViewport)
     return false;
 }
 
+void WebViewImpl::smoothScroll(int targetX, int targetY, long durationMs)
+{
+    IntPoint targetPosition(targetX, targetY);
+    startPageScaleAnimation(targetPosition, false, pageScaleFactor(), (double)durationMs / 1000);
+}
+
 void WebViewImpl::computeScaleAndScrollForFocusedNode(Node* focusedNode, bool zoomInToLegibleScale, float& newScale, IntPoint& newScroll, bool& needAnimation)
 {
     focusedNode->document().updateLayoutIgnorePendingStylesheets();