[promise] make Promise.resolve match spec

src/js/promise.js

Index: src/js/promise.js
diff --git a/src/js/promise.js b/src/js/promise.js
index de9597942c010f52d6dd996fc5faac2000b628ec..041b598764f7b7733284a9a4fc512b6efff2ac2b 100644
--- a/src/js/promise.js
+++ b/src/js/promise.js
@@ -354,11 +354,15 @@ function PromiseThen(onResolve, onReject) {
 // Combinators.
 
 function PromiseCast(x) {
-  if (IsPromise(x) && x.constructor === this) {
-    return x;
-  } else {
-    return new this(function(resolve) { resolve(x) });
+  if (!IS_RECEIVER(this)) {
+    throw MakeTypeError(kCalledOnNonObject, "Promise.resolve");
   }
+
+  if (IsPromise(x) && x.constructor === this) return x;
+
+  var promiseCapability = NewPromiseCapability(this);

[caitp (gmail), 2016/01/04 14:52:11]

Technically, the assertions added in NewPromiseCapability in a separate CL are
important here, and observable in test262 tests fixed in that other CL --- so I
don't think we can take the shortcut as done in the deleted code :(

[Dan Ehrenberg, 2016/01/04 18:04:20]

Yep, I agree. Still looks good to me. The trybot just failed because it needs a
rebase.

+  var resolveResult = promiseCapability.resolve(x);
+  return promiseCapability.promise;
 }
 
 function PromiseAll(iterable) {