[promises] Move PromiseResolveThenableJob to c++

test/mjsunit/es6/promise-thenable-proxy.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.
+
+// Flags: --allow-natives-syntax
+
+function assertAsync(b, s) {
+  if (!b) {
+    %AbortJS(" FAILED!")
+  }
+}
+
+var handler = {
+  get: function(target, name) {
+    if (name === 'then') {
+      return (val) => Promise.prototype.then.call(target, val);
+    }
+  }
+};
+
+var target = new Promise(r => r(42));
+var p = new Proxy(target, handler);
+Promise.resolve(p).then((val) => assertAsync(val === 42));