Date.parse: Add 0 (UTC epoch) test per spec.

test/built-ins/Date/parse/zero.js

@@ -0,0 +1,32 @@
+// Copyright (C) 2018 Andrew Paprocki. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-date.parse
+es6id: 20.3.3.2
+description: >
+  Date.parse of toString/toUTCString/toISOString of zero value is zero
+info: |
+  Date.parse ( string )
+
+  If x is any Date object whose milliseconds amount is zero within a
+  particular implementation of ECMAScript, then all of the following
+  expressions should produce the same numeric value in that
+  implementation, if all the properties referenced have their initial
+  values:
+
+  x.valueOf()
+  Date.parse(x.toString())
+  Date.parse(x.toUTCString())
+  Date.parse(x.toISOString())
+includes: [propertyHelper.js]
+---*/
+
+const zero = new Date(0);
+
+assert.sameValue(zero.valueOf(), Date.parse(zero.toString()),
+                 "Date.parse(zeroDate.toString())");
+assert.sameValue(zero.valueOf(), Date.parse(zero.toUTCString()),
+                 "Date.parse(zeroDate.toUTCString())");
+assert.sameValue(zero.valueOf(), Date.parse(zero.toISOString()),
+                 "Date.parse(zeroDate.toISOString())");