Add support for enabling DCHECKs in release mode

src/utils.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_UTILS_H_
 #define V8_UTILS_H_
 
 #include <limits.h>
 #include <stdlib.h>
 #include <string.h>
@@ skipping 19 matching lines @@
 // Same as strcmp, but can handle NULL arguments.
 inline bool CStringEquals(const char* s1, const char* s2) {
   return (s1 == s2) || (s1 != NULL && s2 != NULL && strcmp(s1, s2) == 0);
 }
 
 
 // X must be a power of 2.  Returns the number of trailing zeros.
 inline int WhichPowerOf2(uint32_t x) {
   DCHECK(base::bits::IsPowerOfTwo32(x));
   int bits = 0;
-#ifdef DEBUG
+#if DCHECK_IS_ON
   int original_x = x;
 #endif
   if (x >= 0x10000) {
     bits += 16;
     x >>= 16;
   }
   if (x >= 0x100) {
     bits += 8;
     x >>= 8;
   }
@@ skipping 1486 matching lines @@
   // Takes the address of the limit variable in order to find out where
   // the top of stack is right now.
   uintptr_t limit = reinterpret_cast<uintptr_t>(&limit);
   return limit;
 }
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_UTILS_H_