Allow assertions to be enabled in Blink Release builds.

Source/wtf/text/StringImpl.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2009 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 409 matching lines @@
     template <class UCharPredicate> PassRefPtr<StringImpl> stripMatchedCharacters(UCharPredicate);
     template <typename CharType, class UCharPredicate> PassRefPtr<StringImpl> simplifyMatchedCharactersToSpace(UCharPredicate, StripBehavior);
     NEVER_INLINE unsigned hashSlowCase() const;
 
 #ifdef STRING_STATS
     static StringStats m_stringStats;
 #endif
 
     static unsigned m_highestStaticStringLength;
 
-#ifndef NDEBUG
+#if ENABLE(ASSERT)
     void assertHashIsCorrect()
     {
         ASSERT(hasHash());
         ASSERT(existingHash() == StringHasher::computeHashAndMaskTop8Bits(characters8(), length()));
     }
 #endif
 
 private:
     unsigned m_refCount;
     unsigned m_length;
@@ skipping 290 matching lines @@
 }
 
 using WTF::StringImpl;
 using WTF::equal;
 using WTF::equalNonNull;
 using WTF::TextCaseSensitivity;
 using WTF::TextCaseSensitive;
 using WTF::TextCaseInsensitive;
 
 #endif