Avoid N^2 walk placing renderers when building the render tree

Source/core/dom/Text.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 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.
  *
@@ skipping 198 matching lines @@
     bool onlyWS = containsOnlyWhitespace();
     if (!onlyWS)
         return true;
 
     RenderObject* parent = context.parentRenderer();
     if (parent->isTable() || parent->isTableRow() || parent->isTableSection() || parent->isRenderTableCol() || parent->isFrameSet())
         return false;
     
     if (context.style()->preserveNewline()) // pre/pre-wrap/pre-line always make renderers.
         return true;
-    
+
+    // FIXME: We should resolve this function's dependencies on next and previous renderers
+    // lazily to avoid potentially N^2 walks through the DOM.
     RenderObject* prev = context.previousRenderer();
     if (prev && prev->isBR()) // <span><br/> <br/></span>
         return false;
         
     if (parent->isRenderInline()) {
         // <span><div/> <div/></span>
         if (prev && !prev->isInline())
             return false;
     } else {
         if (parent->isRenderBlock() && !parent->childrenInline() && (!prev || !prev->isInline()))
@@ skipping 111 matching lines @@
             result.appendLiteral("; ");
         result.appendLiteral("value=");
         result.append(s);
     }
 
     strncpy(buffer, result.toString().utf8().data(), length - 1);
 }
 #endif
 
 } // namespace WebCore