Disable EXTRA_CHECKS in Release

This patch causes V8 to disable EXTRA_CHECKS when building in release. You can
still enable the checks in release using a GYP flag.

This patch speeds up Dromeo's dom-traverse by around 4%.

Review URL: https://codereview.chromium.org/11275324
Patch from Adam Barth <abarth@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12981 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

build/common.gypi

@@ -70,9 +70,6 @@
 
     'v8_enable_disassembler%': 0,
 
-    # Enable extra checks in API functions and other strategic places.
-    'v8_enable_extra_checks%': 1,
-
     'v8_enable_gdbjit%': 0,
 
     'v8_object_print%': 0,
@@ -114,9 +111,6 @@
       ['v8_enable_disassembler==1', {
         'defines': ['ENABLE_DISASSEMBLER',],
       }],
-      ['v8_enable_extra_checks==1', {
-        'defines': ['ENABLE_EXTRA_CHECKS',],
-      }],
       ['v8_enable_gdbjit==1', {
         'defines': ['ENABLE_GDB_JIT_INTERFACE',],
       }],
@@ -336,6 +330,9 @@
     ],  # conditions
     'configurations': {
       'Debug': {
+        'variables': {
+          'v8_enable_extra_checks%': 1,
+        },
         'defines': [
           'DEBUG',
           'ENABLE_DISASSEMBLER',
@@ -360,6 +357,9 @@
           },
         },
         'conditions': [
+          ['v8_enable_extra_checks==1', {
+            'defines': ['ENABLE_EXTRA_CHECKS',],
+          }],
           ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd"', {
             'cflags': [ '-Wall', '<(werror)', '-W', '-Wno-unused-parameter',
                         '-Wnon-virtual-dtor', '-Woverloaded-virtual' ],
@@ -381,7 +381,13 @@
         ],
       },  # Debug
       'Release': {
+        'variables': {
+          'v8_enable_extra_checks%': 0,
+        },
         'conditions': [
+          ['v8_enable_extra_checks==1', {
+            'defines': ['ENABLE_EXTRA_CHECKS',],
+          }],
           ['OS=="linux" or OS=="freebsd" or OS=="openbsd" or OS=="netbsd" \
             or OS=="android"', {
             'cflags!': [