Turn MQ classes into thread safe

Source/wtf/text/StringImpl.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller ( mueller@kde.org )
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Andrew Wellington (proton@wiretapped.net)
  *
  * 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
@@ skipping 1916 matching lines @@
 
     return equal(a->characters16(), b->characters16(), aLength);
 }
 
 bool equal(const StringImpl* a, const StringImpl* b)
 {
     if (a == b)
         return true;
     if (!a || !b)
         return false;
+    if (a->isAtomic() && b->isAtomic())
+        return false;

[abarth-chromium, 2014/03/06 18:52:05]

Can we land this change separately? This code is called from many places and it
would be valuable to measure the performance impact separately.

 
     return stringImplContentEqual(a, b);
 }
 
 template <typename CharType>
 inline bool equalInternal(const StringImpl* a, const CharType* b, unsigned length)
 {
     if (!a)
         return !b;
     if (!b)
@@ skipping 158 matching lines @@
 
 size_t StringImpl::sizeInBytes() const
 {
     size_t size = length();
     if (!is8Bit())
         size *= 2;
     return size + sizeof(*this);
 }
 
 } // namespace WTF