Have Frame::tree() return a reference

Source/core/svg/SVGSVGElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2010 Rob Buis <buis@kde.org>
  * Copyright (C) 2007 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.
  *
@@ skipping 165 matching lines @@
 
 float SVGSVGElement::currentScale() const
 {
     if (!inDocument() || !isOutermostSVGSVGElement())
         return 1;
 
     Frame* frame = document().frame();
     if (!frame)
         return 1;
 
-    FrameTree* frameTree = frame->tree();
-    ASSERT(frameTree);
+    const FrameTree& frameTree = frame->tree();
 
     // The behaviour of currentScale() is undefined, when we're dealing with non-standalone SVG documents.
     // If the svg is embedded, the scaling is handled by the host renderer, so when asking from inside
     // the SVG document, a scale value of 1 seems reasonable, as it doesn't know anything about the parent scale.
-    return frameTree->parent() ? 1 : frame->pageZoomFactor();
+    return frameTree.parent() ? 1 : frame->pageZoomFactor();
 }
 
 void SVGSVGElement::setCurrentScale(float scale)
 {
     if (!inDocument() || !isOutermostSVGSVGElement())
         return;
 
     Frame* frame = document().frame();
     if (!frame)
         return;
 
-    FrameTree* frameTree = frame->tree();
-    ASSERT(frameTree);
+    const FrameTree& frameTree = frame->tree();
 
     // The behaviour of setCurrentScale() is undefined, when we're dealing with non-standalone SVG documents.
     // We choose the ignore this call, it's pretty useless to support calling setCurrentScale() from within
     // an embedded SVG document, for the same reasons as in currentScale() - needs resolution by SVG WG.
-    if (frameTree->parent())
+    if (frameTree.parent())
         return;
 
     frame->setPageZoomFactor(scale);
 }
 
 void SVGSVGElement::setCurrentTranslate(const FloatPoint& translation)
 {
     m_translation = translation;
     updateCurrentTranslate();
 }
@@ skipping 560 matching lines @@
             continue;
 
         Element* element = toElement(node);
         if (element->getIdAttribute() == id)
             return element;
     }
     return 0;
 }
 
 }