Allow JavaScript accessors on API objects.

build/features.gypi

Index: build/features.gypi
diff --git a/build/features.gypi b/build/features.gypi
index 86b351105eed92e1f42b18e12184c1d9eeb5e27f..f7bf57d684971b2299b3b3eaf7738d74c8fe4bba 100644
--- a/build/features.gypi
+++ b/build/features.gypi
@@ -67,6 +67,9 @@
 
     # Set to 1 to enable building with wasm prototype.
     'v8_wasm%': 0,
+
+    # Enable/disable JavaScript API accessors.
+    'v8_js_accessors%': 0,
   },
   'target_defaults': {
     'conditions': [
@@ -109,6 +112,9 @@
       ['v8_wasm!=0', {
         'defines': ['V8_WASM',],
       }],
+      ['v8_js_accessors!=0', {
+        'defines': ['V8_JS_ACCESSORS'],
+      }],
     ],  # conditions
     'configurations': {
       'DebugBaseCommon': {