Make StringImpl's content immutable

third_party/WebKit/Source/wtf/text/StringBuilder.cpp

 /*
  * Copyright (C) 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2012 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:
  * 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 39 matching lines @@
         m_string = StringImpl::empty();
         return;
     }
 
     ASSERT(m_buffer && m_length <= m_buffer->length());
     if (m_length == m_buffer->length()) {
         m_string = m_buffer.release();
         return;
     }
 
-    if (m_buffer->hasOneRef()) {
-        m_buffer->truncateAssumingIsolated(m_length);
-        m_string = m_buffer.release();
-        return;
-    }
-
     m_string = m_buffer->substring(0, m_length);
 }
 
 String StringBuilder::reifySubstring(unsigned position, unsigned length) const
 {
     ASSERT(m_string.isNull());
     ASSERT(m_buffer);
     unsigned substringLength = std::min(length, m_length - position);
     return m_buffer->substring(position, substringLength);
 }
@@ skipping 306 matching lines @@
     if (!canShrink())
         return;
     if (m_is8Bit)
         reallocateBuffer<LChar>(m_length);
     else
         reallocateBuffer<UChar>(m_length);
     m_string = m_buffer.release();
 }
 
 } // namespace WTF