added coverage for built-in Map spec to ensure that a TypeError is thrown when...

added coverage for built-in Map spec to ensure that a TypeError is thrown when Symbol.iterator is undefined (#1444)

test/built-ins/Map/iterator-is-undefined-throws.js

+// Copyright (C) 2018 Amal Hussein. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+/*---
+esid: sec-map-objects
+description: >
+  Throws a TypeError if the iterator of the iterable is undefined.
+info: |
+  Map ( [ iterable ] )
+  ...
+  9. Let iteratorRecord be ? GetIterator(iterable).
+features: [Symbol.iterator]
+---*/
+
+var iterable  = { [Symbol.iterator]: undefined };
+
+assert.throws(TypeError,
+  function () {
+    new Map(iterable);
+});