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

Source/core/rendering/RenderBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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
@@ skipping 450 matching lines @@
         parentBox = parent()->enclosingBox();
         restrictedByLineClamp = !parent()->style()->lineClamp().isNone();
     }
 
     if (hasOverflowClip() && !restrictedByLineClamp) {
         // Don't scroll to reveal an overflow layer that is restricted by the -webkit-line-clamp property.
         // This will prevent us from revealing text hidden by the slider in Safari RSS.
         newRect = layer()->scrollableArea()->exposeRect(rect, alignX, alignY);
     } else if (!parentBox && canBeProgramaticallyScrolled()) {
         if (FrameView* frameView = this->frameView()) {
-            Element* ownerElement = document().ownerElement();
+            HTMLFrameOwnerElement* ownerElement = document().ownerElement();
 
             if (ownerElement && ownerElement->renderer()) {
-                HTMLFrameElementBase* frameElementBase = 0;
-
-                if (isHTMLFrameElement(*ownerElement) || isHTMLIFrameElement(*ownerElement))
-                    frameElementBase = toHTMLFrameElementBase(ownerElement);
-
+                HTMLFrameElementBase* frameElementBase = isHTMLFrameElementBase(*ownerElement) ? toHTMLFrameElementBase(ownerElement) : 0;
                 if (frameElementAndViewPermitScroll(frameElementBase, frameView)) {
                     LayoutRect viewRect = frameView->visibleContentRect();
                     LayoutRect exposeRect = ScrollAlignment::getRectToExpose(viewRect, rect, alignX, alignY);
 
                     int xOffset = roundToInt(exposeRect.x());
                     int yOffset = roundToInt(exposeRect.y());
                     // Adjust offsets if they're outside of the allowable range.
                     xOffset = std::max(0, std::min(frameView->contentsWidth(), xOffset));
                     yOffset = std::max(0, std::min(frameView->contentsHeight(), yOffset));
 
@@ skipping 4209 matching lines @@
 RenderBox::BoxDecorationData::BoxDecorationData(const RenderStyle& style)
 {
     backgroundColor = style.visitedDependentColor(CSSPropertyBackgroundColor);
     hasBackground = backgroundColor.alpha() || style.hasBackgroundImage();
     ASSERT(hasBackground == style.hasBackground());
     hasBorder = style.hasBorder();
     hasAppearance = style.hasAppearance();
 }
 
 } // namespace blink