Have Frame::tree() return a reference

Source/core/loader/TextResourceDecoderBuilder.cpp

 /*
  * Copyright (C) 2013 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 51 matching lines @@
         if (Settings* settings = frame->settings())
             return TextResourceDecoder::create(m_mimeType, settings->defaultTextEncodingName(), settings->usesEncodingDetector());
     }
 
     return TextResourceDecoder::create(m_mimeType, String());
 }
 
 inline void TextResourceDecoderBuilder::setupEncoding(TextResourceDecoder* decoder, Document* document)
 {
     Frame* frame = document->frame();
-    Frame* parentFrame = frame ? frame->tree()->parent() : 0;
+    Frame* parentFrame = frame ? frame->tree().parent() : 0;
 
     if (!m_encoding.isEmpty())
         decoder->setEncoding(m_encoding, m_encodingWasChosenByUser ? TextResourceDecoder::UserChosenEncoding : TextResourceDecoder::EncodingFromHTTPHeader);
 
     // Set the hint encoding to the parent frame encoding only if
     // the parent and the current frames share the security origin.
     // We impose this condition because somebody can make a child frameg63
     // containing a carefully crafted html/javascript in one encoding
     // that can be mistaken for hintEncoding (or related encoding) by
     // an auto detector. When interpreted in the latter, it could be
@@ skipping 15 matching lines @@
     return decoder.release();
 }
 
 void TextResourceDecoderBuilder::clear()
 {
     if (!m_encodingWasChosenByUser)
         m_encoding = String();
 }
 
 }