Remove AtomicStringImpl.

Source/wtf/text/AtomicString.cpp

 /*
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Patrick Gansterer <paroga@paroga.com>
  * Copyright (C) 2012 Google 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 379 matching lines @@
     return result;
 }
 
 template<typename CharacterType>
 static inline HashSet<StringImpl*>::iterator findString(const StringImpl* stringImpl)
 {
     HashAndCharacters<CharacterType> buffer = { stringImpl->existingHash(), stringImpl->getCharacters<CharacterType>(), stringImpl->length() };
     return stringTable().find<HashAndCharactersTranslator<CharacterType> >(buffer);
 }
 
-AtomicStringImpl* AtomicString::find(const StringImpl* stringImpl)
+StringImpl* AtomicString::find(const StringImpl* stringImpl)
 {
     ASSERT(stringImpl);
     ASSERT(stringImpl->existingHash());
 
     if (!stringImpl->length())
-        return static_cast<AtomicStringImpl*>(StringImpl::empty());
+        return StringImpl::empty();
 
     HashSet<StringImpl*>::iterator iterator;
     if (stringImpl->is8Bit())
         iterator = findString<LChar>(stringImpl);
     else
         iterator = findString<UChar>(stringImpl);
     if (iterator == stringTable().end())
         return 0;
-    return static_cast<AtomicStringImpl*>(*iterator);
+    return *iterator;
 }
 
 void AtomicString::remove(StringImpl* r)
 {
     HashSet<StringImpl*>::iterator iterator;
     if (r->is8Bit())
         iterator = findString<LChar>(r);
     else
         iterator = findString<UChar>(r);
     RELEASE_ASSERT(iterator != stringTable().end());
@@ skipping 27 matching lines @@
 }
 
 #ifndef NDEBUG
 void AtomicString::show() const
 {
     m_string.show();
 }
 #endif
 
 } // namespace WTF