Turn on DCHECKs and other debugging code if dcheck_always_on is 1

build/toolchain.gypi

 # Copyright 2013 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 885 matching lines @@
               '-fdata-sections',
               '-ffunction-sections',
             ],
           }],
           ['OS=="mac"', {
             'xcode_settings': {
                'GCC_OPTIMIZATION_LEVEL': '0',  # -O0
             },
           }],
         ],
+        'defines': [
+          'ENABLE_SLOW_DCHECKS',
+        ],
       },  # DebugBase0
       # Abstract configuration for v8_optimized_debug == 1.
       'DebugBase1': {
         'abstract': 1,
         'msvs_settings': {
           'VCCLCompilerTool': {
             'Optimization': '1',
             'InlineFunctionExpansion': '2',
             'EnableIntrinsicFunctions': 'true',
             'FavorSizeOrSpeed': '0',
             'StringPooling': 'true',
             'BasicRuntimeChecks': '0',
             'conditions': [
               ['component=="shared_library"', {
                 'RuntimeLibrary': '3',  # /MDd
               }, {
                 'RuntimeLibrary': '1',  # /MTd
               }],
             ],
           },
           'VCLinkerTool': {
             'LinkIncremental': '2',
           },
         },
+        'defines': [
+          'ENABLE_SLOW_DCHECKS',
+        ],
         'conditions': [
           ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd" or \
             OS=="qnx"', {
             'cflags!': [
               '-O0',
               '-O3', # TODO(2807) should be -O1.
               '-O2',
               '-Os',
             ],
             'cflags': [
@@ skipping 40 matching lines @@
             OS=="qnx"', {
             'cflags!': [
               '-O0',
               '-O1',
               '-Os',
             ],
             'cflags': [
               '-fdata-sections',
               '-ffunction-sections',
             ],
-            'defines': [
-              'OPTIMIZED_DEBUG'
-            ],
             'conditions': [
               # TODO(crbug.com/272548): Avoid -O3 in NaCl
               ['nacl_target_arch=="none"', {
                 'cflags': ['-O3'],
                 'cflags!': ['-O2'],
                 }, {
                 'cflags': ['-O2'],
                 'cflags!': ['-O3'],
               }],
             ],
@@ skipping 121 matching lines @@
                 'OptimizeReferences': '2',
                 'EnableCOMDATFolding': '2',
               },
             },
           }],  # OS=="win"
         ],  # conditions
       },  # Release
     },  # configurations
   },  # target_defaults
 }