change of V8_DEPRECATED to be enabled behind a gyp flag

build/features.gypi

Index: build/features.gypi
diff --git a/build/features.gypi b/build/features.gypi
index 5343284dbc987958368807f65a797af134d6a2cf..9af58c34dca037a853bc3f88ebc0c8458ad34304 100644
--- a/build/features.gypi
+++ b/build/features.gypi
@@ -55,6 +55,9 @@
     # Enable ECMAScript Internationalization API. Enabling this feature will
     # add a dependency on the ICU library.
     'v8_enable_i18n_support%': 1,
+
+    # Enable compiler warnings when using V8_DEPRECATED apis.
+    'v8_deprecation_warnings%': 0,
   },
   'target_defaults': {
     'conditions': [
@@ -76,6 +79,9 @@
       ['v8_interpreted_regexp==1', {
         'defines': ['V8_INTERPRETED_REGEXP',],
       }],
+      ['v8_deprecation_warnings==1', {
+        'defines': ['V8_DEPRECATION_WARNINGS',],
+      }],
       ['v8_enable_i18n_support==1', {
         'defines': ['V8_I18N_SUPPORT',],
       }],