Add reference tests for trimLeft and trimRight

test/annexB/built-ins/String/prototype/trimLeft/reference-trimStart.js

+// Copyright (C) 2017 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-string.prototype.trimLeft
+description: >
+  String.prototype.trimLeft is a reference to String.prototype.trimStart.
+info: >
+  String.prototype.trimLeft ( )
+
+  The function object that is the initial value of String.prototype.trimLeft
+  is the same function object that is the initial value of
+  String.prototype.trimStart.
+features: [string-trimming]
+---*/
+
+assert.sameValue(String.prototype.trimLeft, String.prototype.trimStart);

test/annexB/built-ins/String/prototype/trimRight/reference-trimEnd.js

+// Copyright (C) 2017 Valerie Young. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-string.prototype.trimRight
+description: >
+  String.prototype.trimRight is a reference to String.prototype.trimEnd.
+info: >
+  String.prototype.trimRight ( )
+
+  The function object that is the initial value of String.prototype.trimRight
+  is the same function object that is the initial value of
+  String.prototype.trimEnd.
+features: [string-trimming]
+---*/
+
+assert.sameValue(String.prototype.trimRight, String.prototype.trimEnd);