Make StringImpl's content immutable

third_party/WebKit/Source/wtf/text/StringBuffer.h

 /*
  * Copyright (C) 2008, 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
@@ skipping 52 matching lines @@
 private:
     RefPtr<StringImpl> m_data;
 };
 
 template <typename CharType>
 void StringBuffer<CharType>::shrink(unsigned newLength)
 {
     ASSERT(m_data);
     if (m_data->length() == newLength)
         return;
-    m_data->truncateAssumingIsolated(newLength);
+    m_data = m_data->substring(0, newLength);
 }
 
 } // namespace WTF
 
 using WTF::StringBuffer;
 
 #endif // StringBuffer_h