Add V8 extra utils for promise state

src/js/prologue.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function(global, utils, extrasUtils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
@@ skipping 200 matching lines @@
 
 // We pass true to trigger the debugger's on exception handler.
 extrasUtils.rejectPromise = function rejectPromise(promise, reason) {
   %promise_internal_reject(promise, reason, true);
 }
 
 extrasUtils.markPromiseAsHandled = function markPromiseAsHandled(promise) {
   %PromiseMarkAsHandled(promise);
 };
 
+extrasUtils.promiseState = function promiseState(promise) {
+  return %PromiseStatus(promise);

[Dan Ehrenberg, 2017/03/30 12:05:53]

Is it OK for V8 extras to crash when not-a-promise is passed in here, or should
it throw a neat exception?

+};
+
+// [[PromiseState]] values (for extrasUtils.promiseState())
+// These values should be kept in sync with PromiseStatus in globals.h
+extrasUtils.kPROMISE_PENDING = 0;
+extrasUtils.kPROMISE_FULFILLED = 1;
+extrasUtils.kPROMISE_REJECTED = 2;
+
 %ToFastProperties(extrasUtils);
 
 })