Use tighter typing for Document::ownerElement() return value

Source/core/rendering/RenderView.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 435 matching lines @@
 
 void RenderView::invalidatePaintForRectangle(const LayoutRect& paintInvalidationRect) const
 {
     ASSERT(!paintInvalidationRect.isEmpty());
 
     if (document().printing() || !m_frameView)
         return;
 
     // We always just invalidate the root view, since we could be an iframe that is clipped out
     // or even invisible.
-    Element* owner = document().ownerElement();
+    HTMLFrameOwnerElement* owner = document().ownerElement();
     if (layer()->compositingState() == PaintsIntoOwnBacking) {
         layer()->paintInvalidator().setBackingNeedsPaintInvalidationInRect(paintInvalidationRect);
     } else if (!owner) {
         m_frameView->contentRectangleForPaintInvalidation(pixelSnappedIntRect(paintInvalidationRect));
     } else if (RenderBox* obj = owner->renderBox()) {
         // Intersect the viewport with the paint invalidation rect.
         LayoutRect viewRectangle = viewRect();
         LayoutRect rectToInvalidate = intersection(paintInvalidationRect, viewRectangle);
 
         // Adjust for scroll offset of the view.
@@ skipping 514 matching lines @@
     return viewWidth(IncludeScrollbars) / scale;
 }
 
 double RenderView::layoutViewportHeight() const
 {
     float scale = m_frameView ? m_frameView->frame().pageZoomFactor() : 1;
     return viewHeight(IncludeScrollbars) / scale;
 }
 
 } // namespace blink