[promise] Spec compliance fixes for async/await

src/js/promise.js

Index: src/js/promise.js
diff --git a/src/js/promise.js b/src/js/promise.js
index 20ffc8c4892327ac68f5242c7900a1006303959e..54058b792bd7ad41b94e271df9b6b37a5599bb40 100644
--- a/src/js/promise.js
+++ b/src/js/promise.js
@@ -386,8 +386,14 @@ function PromiseCreateRejected(r) {
   return %_Call(PromiseReject, GlobalPromise, r);
 }
 
-function PromiseCreateResolved(x) {
-  return %_Call(PromiseResolve, GlobalPromise, x);
+function PromiseCreateResolved(value) {
+  if (IsPromise(value)) {
+    return value;

[caitp, 2016/08/05 00:43:43]

looks great. Should we do something similar for PromiseCreateRejected? I haven't
checked

[Dan Ehrenberg, 2016/08/05 01:22:36]

I don't think we need to optimize for the reject case, and it's not needed from
a correctness perspective because rejecting a Promise doesn't collapse/chain in
any particular way.

+  } else {
+    var promise = PromiseInit(new GlobalPromise(promiseRawSymbol));
+    var resolveResult = ResolvePromise(promise, value);
+    return promise;
+  }
 }
 
 function PerformPromiseThen(promise, onResolve, onReject, resultCapability) {
@@ -629,8 +635,6 @@ utils.InstallFunctions(extrasUtils, 0, [
     fn => %FunctionRemovePrototype(fn));
 
 utils.Export(function(to) {
-  to.IsPromise = IsPromise;
-
   to.PromiseChain = PromiseChain;
   to.PromiseDefer = PromiseDefer;
   to.PromiseAccept = PromiseAccept;