Add build system infrastructure for ENABLE_EXTRA_CHECKS flag (not used yet)

build/common.gypi

 # Copyright 2012 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 52 matching lines @@
     # Similar to the ARM hard float ABI but on MIPS.
     'v8_use_mips_abi_hardfloat%': 'true',
 
     # Default arch variant for MIPS.
     'mips_arch_variant%': 'mips32r2',
 
     'v8_enable_debugger_support%': 1,
 
     'v8_enable_disassembler%': 0,
 
+    # Enable extra checks in API functions and other strategic places.
+    'v8_enable_extra_checks%' 1,
+
     'v8_object_print%': 0,
 
     'v8_enable_gdbjit%': 0,
 
     # Enable profiling support. Only required on Windows.
     'v8_enable_prof%': 0,
 
     # Some versions of GCC 4.5 seem to need -fno-strict-aliasing.
     'v8_no_strict_aliasing%': 0,
 
@@ skipping 19 matching lines @@
     'v8_interpreted_regexp%': 0,
   },
   'target_defaults': {
     'conditions': [
       ['v8_enable_debugger_support==1', {
         'defines': ['ENABLE_DEBUGGER_SUPPORT',],
       }],
       ['v8_enable_disassembler==1', {
         'defines': ['ENABLE_DISASSEMBLER',],
       }],
+      ['v8_enable_extra_checks==1', {
+        'defines': ['ENABLE_EXTRA_CHECKS',],
+      }],
       ['v8_object_print==1', {
         'defines': ['OBJECT_PRINT',],
       }],
       ['v8_enable_gdbjit==1', {
         'defines': ['ENABLE_GDB_JIT_INTERFACE',],
       }],
       ['v8_interpreted_regexp==1', {
         'defines': ['V8_INTERPRETED_REGEXP',],
       }],
       ['v8_target_arch=="arm"', {
@@ skipping 293 matching lines @@
                 'OptimizeReferences': '2',
                 'EnableCOMDATFolding': '2',
               },
             },
           }],  # OS=="win"
         ],  # conditions
       },  # Release
     },  # configurations
   },  # target_defaults
 }