intl: increase coverage for DateTimeFormat

Increase coverage for the Intl.DateTimeFormat constructor by adding a
test that confirms that ToObject(...) is appropriately called inside the
implementation.

test/intl402/DateTimeFormat/constructor-options-toobject.js

@@ -0,0 +1,42 @@
+// Copyright (C) 2018 Ujjwal Sharma. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-initializedatetimeformat
+description: >
+  Tests that Intl.DateTimeFormat contructor converts the options argument
+  to an object using `ToObject` (7.1.13).
+info: |
+  12.1.2 ToDateTimeOptions
+
+  1. If options is undefined, let options be null; otherwise let options be ?
+  ToObject(options).
+---*/
+
+const toObjectResults = [
+  [true, new Boolean(true)],
+  [42, new Number(42)],
+  ['foo', new String('foo')],
+  [{}, {}],
+  [Symbol(), Object(Symbol())]
+];
+
+// Test if ToObject is used to convert primitives to Objects.
+toObjectResults.forEach(pair => {
+  const [value, result] = pair;
+
+  const actual = new Intl.DateTimeFormat(['en-US'], value).resolvedOptions();
+  const expected = new Intl.DateTimeFormat(['en-US'], result).resolvedOptions();
+
+  assert.sameValue(actual.locale, expected.locale);
+  assert.sameValue(actual.calendar, expected.calendar);
+  assert.sameValue(actual.day, expected.day);
+  assert.sameValue(actual.month, expected.month);
+  assert.sameValue(actual.year, expected.year);
+  assert.sameValue(actual.numberingSystem, expected.numberingSystem);
+  assert.sameValue(actual.timeZone, expected.timeZone);
+});
+
+// ToObject throws a TypeError for undefined and null, but it's not called
+// when options is undefined.
+assert.throws(TypeError, () => new Intl.DateTimeFormat(['en-US'], null));