Introduce a handle zapping setting, and enable it by default for release and debug

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index dbb33a867bfb9abd6aaeb88a542aa69b168c082d..f73c8812f0a673ff81d812357120bb6bbf364fce 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -490,6 +490,7 @@
       'Debug': {
         'variables': {
           'v8_enable_extra_checks%': 1,
+          'v8_enable_handle_zapping%': 1,
         },
         'defines': [
           'DEBUG',
@@ -518,6 +519,9 @@
           ['v8_enable_extra_checks==1', {
             'defines': ['ENABLE_EXTRA_CHECKS',],
           }],
+          ['v8_enable_handle_zapping==1', {
+            'defines': ['ENABLE_HANDLE_ZAPPING',],
+          }],
           ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd"', {
             'cflags': [ '-Wall', '<(werror)', '-W', '-Wno-unused-parameter',
                         '-Wnon-virtual-dtor', '-Woverloaded-virtual' ],
@@ -550,11 +554,15 @@
       'Release': {
         'variables': {
           'v8_enable_extra_checks%': 0,
+          'v8_enable_handle_zapping%': 1,
         },
         'conditions': [
           ['v8_enable_extra_checks==1', {
             'defines': ['ENABLE_EXTRA_CHECKS',],
           }],
+          ['v8_enable_handle_zapping==1', {
+            'defines': ['ENABLE_HANDLE_ZAPPING',],
+          }],
           ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd"', {
             'cflags!': [
               '-O2',