[promises] update comment about deferred reactions symbol state

src/js/promise.js

 // Copyright 2012 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 110 matching lines @@
   // 1) UNDEFINED -- This is the zero state where there is no callback
   // registered. When we see this state, we directly attach the callbacks to
   // the symbol.
   // 2) !IS_ARRAY -- There is a single callback directly attached to the
   // symbols. We need to create a new array to store additional callbacks.
   // 3) IS_ARRAY -- There are multiple callbacks already registered,
   // therefore we can just push the new callback to the existing array.
   SET_PRIVATE(promise, promiseFulfillReactionsSymbol, UNDEFINED);
   SET_PRIVATE(promise, promiseRejectReactionsSymbol, UNDEFINED);
 
-  // There are 2 possible states for this symbol --
-  // 1) UNDEFINED -- This is the zero state, no deferred object is
-  // attached to this symbol. When we want to add a new deferred we
-  // directly attach it to this symbol.
-  // 2) symbol with attached deferred object -- New deferred objects
-  // are not attached to this symbol, but instead they are directly
-  // attached to the resolve, reject callback arrays. At this point,
-  // the deferred symbol's state is stale, and the deferreds should be
-  // read from the reject, resolve callbacks.
+  // This symbol is used only when one deferred needs to be attached. When more
+  // than one deferred need to be attached the promise, we attach them directly
+  // to the promiseFulfillReactionsSymbol and promiseRejectReactionsSymbol and
+  // reset this back to UNDEFINED.
   SET_PRIVATE(promise, promiseDeferredReactionsSymbol, UNDEFINED);

[adamk, 2016/10/10 19:19:32]

Can you rename the symbol to match its usage? And change the callers to stop
using a plural for variables that are assigned the value of this symbol (I see
"deferreds = ..." in several places)

 
   return promise;
 }
 
 function PromiseCreateAndSet(status, value) {
   var promise = new GlobalPromise(promiseRawSymbol);
   // If debug is active, notify about the newly created promise first.
   if (DEBUG_IS_ACTIVE) PromiseSet(promise, kPending, UNDEFINED);
   return PromiseSet(promise, status, value);
 }
@@ skipping 571 matching lines @@
   to.PromiseNextMicrotaskID = PromiseNextMicrotaskID;
 
   to.GlobalPromise = GlobalPromise;
   to.NewPromiseCapability = NewPromiseCapability;
   to.PerformPromiseThen = PerformPromiseThen;
   to.ResolvePromise = ResolvePromise;
   to.RejectPromise = RejectPromise;
 });
 
 })