Have Frame::tree() return a reference

Source/core/rendering/RenderLayerCompositor.cpp

 /*
  * Copyright (C) 2009, 2010 Apple 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 430 matching lines @@
     }
 
 #if !LOG_DISABLED
     if (compositingLogEnabled() && isFullUpdate && (needHierarchyUpdate || needGeometryUpdate)) {
         m_obligateCompositedLayerCount = 0;
         m_secondaryCompositedLayerCount = 0;
         m_obligatoryBackingStoreBytes = 0;
         m_secondaryBackingStoreBytes = 0;
 
         Frame& frame = m_renderView->frameView()->frame();
-        LOG(Compositing, "\nUpdate %d of %s.\n", m_rootLayerUpdateCount, isMainFrame() ? "main frame" : frame.tree()->uniqueName().string().utf8().data());
+        LOG(Compositing, "\nUpdate %d of %s.\n", m_rootLayerUpdateCount, isMainFrame() ? "main frame" : frame.tree().uniqueName().string().utf8().data());
     }
 #endif
 
     if (needHierarchyUpdate) {
         // Update the hierarchy of the compositing layers.
         Vector<GraphicsLayer*> childList;
         {
             TRACE_EVENT0("blink_rendering", "RenderLayerCompositor::rebuildCompositingLayerTree");
             rebuildCompositingLayerTree(updateRoot, childList, 0);
         }
@@ skipping 2107 matching lines @@
 
 // IFrames are special, because we hook compositing layers together across iframe boundaries
 // when both parent and iframe content are composited. So when this frame becomes composited, we have
 // to use a synthetic style change to get the iframes into RenderLayers in order to allow them to composite.
 void RenderLayerCompositor::notifyIFramesOfCompositingChange()
 {
     if (!m_renderView->frameView())
         return;
     Frame& frame = m_renderView->frameView()->frame();
 
-    for (Frame* child = frame.tree()->firstChild(); child; child = child->tree()->traverseNext(&frame)) {
+    for (Frame* child = frame.tree().firstChild(); child; child = child->tree().traverseNext(&frame)) {
         if (child->document() && child->document()->ownerElement())
             child->document()->ownerElement()->scheduleLayerUpdate();
     }
 
     // Compositing also affects the answer to RenderIFrame::requiresAcceleratedCompositing(), so
     // we need to schedule a style recalc in our parent document.
     if (HTMLFrameOwnerElement* ownerElement = m_renderView->document().ownerElement())
         ownerElement->scheduleLayerUpdate();
 }
 
@@ skipping 185 matching lines @@
     } else if (graphicsLayer == m_scrollLayer.get()) {
         name = "Frame Scrolling Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace WebCore