Have Frame::tree() return a reference

Source/core/rendering/TextAutosizer.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  * Copyright (C) 2012 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 169 matching lines @@
     TextAutosizingWindowInfo windowInfo;
 
     // Window area, in logical (density-independent) pixels.
     windowInfo.windowSize = m_document->settings()->textAutosizingWindowSizeOverride();
     if (windowInfo.windowSize.isEmpty())
         windowInfo.windowSize = mainFrame->view()->unscaledVisibleContentSize(ScrollableArea::IncludeScrollbars);
 
     // Largest area of block that can be visible at once (assuming the main
     // frame doesn't get scaled to less than overview scale), in CSS pixels.
     windowInfo.minLayoutSize = mainFrame->view()->layoutSize();
-    for (Frame* frame = m_document->frame(); frame; frame = frame->tree()->parent())
+    for (Frame* frame = m_document->frame(); frame; frame = frame->tree().parent())
         windowInfo.minLayoutSize = windowInfo.minLayoutSize.shrunkTo(frame->view()->layoutSize());
 
     // The layoutRoot could be neither a container nor a cluster, so walk up the tree till we find each of these.
     RenderBlock* container = layoutRoot->isRenderBlock() ? toRenderBlock(layoutRoot) : layoutRoot->containingBlock();
     while (container && !isAutosizingContainer(container))
         container = container->containingBlock();
 
     RenderBlock* cluster = container;
     while (cluster && (!isAutosizingContainer(cluster) || !isIndependentDescendant(cluster)))
         cluster = cluster->containingBlock();
@@ skipping 529 matching lines @@
         if (i + 1 < clusterInfos.size()) {
             float currentWidth = clusterInfos[i].root->contentLogicalWidth();
             float nextWidth = clusterInfos[i + 1].root->contentLogicalWidth();
             if (currentWidth - nextWidth > maxWidthDifferenceWithinGroup)
                 groups.grow(groups.size() + 1);
         }
     }
 }
 
 } // namespace WebCore