Enable assertions and debugging code in the release...

tools/gyp/v8.gyp

 # Copyright 2009 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 59 matching lines @@
           'VCCLCompilerTool': {
             'Optimizations': '0',
             'RuntimeLibrary': '1',
           },
           'VCLinkerTool': {
             'LinkIncremental': '2',
           },
         },
       },
       'Release': {
+        'defines': [
+          'DEBUG',
+          '_DEBUG'
+        ],
         'conditions': [
           ['OS=="linux"', {
             'cflags!': [
               '-O2',
               '-Os',
             ],
             'cflags': [
               '-fomit-frame-pointer',
               '-O3',
             ],
@@ skipping 521 matching lines @@
       ],
       'conditions': [
         [ 'OS=="win"', {
           # This could be gotten by not setting chromium_code, if that's OK.
           'defines': ['_CRT_SECURE_NO_WARNINGS'],
         }],
       ],
     },
   ],
 }