Enable ASSERT when DCHECK_ALWAYS_ON is defined.

Source/wtf/Assertions.h

 /*
  * Copyright (C) 2003, 2006, 2007 Apple Inc.  All rights reserved.
  * Copyright (C) 2013 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 25 matching lines @@
    For non-debug builds, everything is disabled by default, except for the
    RELEASE_ASSERT family of macros.
 
    Defining any of the symbols explicitly prevents this from having any effect.
 
 */
 
 #include "wtf/Compiler.h"
 #include "wtf/WTFExport.h"
 
+#ifndef ASSERTIONS_DISABLED_DEFAULT
 #ifdef NDEBUG
 /* Disable ASSERT* macros in release mode. */
 #define ASSERTIONS_DISABLED_DEFAULT 1
 #else
 #define ASSERTIONS_DISABLED_DEFAULT 0
 #endif
+#endif
 
 #ifndef BACKTRACE_DISABLED
 #define BACKTRACE_DISABLED ASSERTIONS_DISABLED_DEFAULT
 #endif
 
 #ifndef ASSERT_DISABLED
 #define ASSERT_DISABLED ASSERTIONS_DISABLED_DEFAULT
 #endif
 
 #ifndef ASSERT_MSG_DISABLED
@@ skipping 329 matching lines @@
 } \
 inline const thisType& to##thisType(const argumentType& argumentName) \
 { \
     ASSERT_WITH_SECURITY_IMPLICATION(referencePredicate); \
     return static_cast<const thisType&>(argumentName); \
 } \
 void to##thisType(const thisType*); \
 void to##thisType(const thisType&)
 
 #endif /* WTF_Assertions_h */