Add WebView API for smoothScroll

Source/web/WebViewImpl.h

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 165 matching lines @@
     void setWindowFeatures(const WebWindowFeatures&) override;
     void setOpenedByDOM() override;
     WebFrame* mainFrame() override;
     WebFrame* findFrameByName(
         const WebString& name, WebFrame* relativeToFrame) override;
     WebFrame* focusedFrame() override;
     void setFocusedFrame(WebFrame*) override;
     void setInitialFocus(bool reverse) override;
     void clearFocusedElement() override;
     bool scrollFocusedNodeIntoRect(const WebRect&) override;
+    void smoothScroll(int targetX, int targetY, long durationMs) override;
     void zoomToFindInPageRect(const WebRect&);
     void advanceFocus(bool reverse) override;
     double zoomLevel() override;
     double setZoomLevel(double) override;
     void zoomLimitsChanged(double minimumZoomLevel, double maximumZoomLevel) override;
     float textZoomFactor() override;
     float setTextZoomFactor(float) override;
     bool zoomToMultipleTargetsRect(const WebRect&) override;
     float pageScaleFactor() const override;
     void setDefaultPageScaleLimits(float minScale, float maxScale) override;
@@ skipping 564 matching lines @@
 };
 
 DEFINE_TYPE_CASTS(WebViewImpl, WebWidget, widget, widget->isWebView(), widget.isWebView());
 // We have no ways to check if the specified WebView is an instance of
 // WebViewImpl because WebViewImpl is the only implementation of WebView.
 DEFINE_TYPE_CASTS(WebViewImpl, WebView, webView, true, true);
 
 } // namespace blink
 
 #endif