Disable non-standard Promise functions in staging

src/js/promise.js

Index: src/js/promise.js
diff --git a/src/js/promise.js b/src/js/promise.js
index f0c9bb3b520ca1bda70fff1ad1f3baae3933a00d..794f57b6fc0f3197e8f8d8651c9414fb7dcc3f5c 100644
--- a/src/js/promise.js
+++ b/src/js/promise.js
@@ -446,8 +446,6 @@ function PromiseHasUserDefinedRejectHandler() {
                   DONT_ENUM | READ_ONLY);
 
 utils.InstallFunctions(GlobalPromise, DONT_ENUM, [
-  "defer", PromiseDeferred,
-  "accept", PromiseResolved,
   "reject", PromiseRejected,
   "all", PromiseAll,
   "race", PromiseRace,
@@ -455,14 +453,12 @@ utils.InstallFunctions(GlobalPromise, DONT_ENUM, [
 ]);
 
 utils.InstallFunctions(GlobalPromise.prototype, DONT_ENUM, [
-  "chain", PromiseChain,
   "then", PromiseThen,
   "catch", PromiseCatch
 ]);
 
 %InstallToContext([
   "promise_catch", PromiseCatch,
-  "promise_chain", PromiseChain,
   "promise_create", PromiseCreate,
   "promise_has_user_defined_reject_handler", PromiseHasUserDefinedRejectHandler,
   "promise_reject", PromiseReject,
@@ -479,4 +475,14 @@ utils.InstallFunctions(extrasUtils, 0, [
   "rejectPromise", PromiseReject
 ]);
 
+// TODO(v8:4567): Allow experimental natives to remove function prototype
+[PromiseChain, PromiseDeferred, PromiseResolved].forEach(
+    fn => %FunctionRemovePrototype(fn));
+
+utils.Export(function(to) {
+  to.PromiseChain = PromiseChain;
+  to.PromiseDeferred = PromiseDeferred;
+  to.PromiseResolved = PromiseResolved;
+});
+
 })