Add basic Symbol constructor tests (#1069)

* add Symbol.length test

* add Symbol.name test

* add global.Symbol test

test/built-ins/Symbol/length.js

+// Copyright (C) 2017 Aleksey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-symbol-constructor
+description: >
+  Properties of the Symbol Constructor
+
+  Besides the length property (whose value is 0)
+
+includes: [propertyHelper.js]
+---*/
+
+assert.sameValue(Symbol.length, 0, "The value of `Symbol.length` is `0`");
+
+verifyNotEnumerable(Symbol, "length");
+verifyNotWritable(Symbol, "length");
+verifyConfigurable(Symbol, "length");

test/built-ins/Symbol/name.js

+// Copyright (C) 2017 Aleksey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-symbol-constructor
+description: >
+  Symbol ( [ description ] )
+
+includes: [propertyHelper.js]
+---*/
+
+assert.sameValue(Symbol.name, "Symbol", "The value of `Symbol.name` is `'Symbol'`");
+
+verifyNotEnumerable(Symbol, "name");
+verifyNotWritable(Symbol, "name");
+verifyConfigurable(Symbol, "name");

test/built-ins/Symbol/symbol.js

+// Copyright (C) 2017 Aleksey Shvayka. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+esid: sec-symbol-constructor
+description: >
+  The Symbol constructor is the %Symbol% intrinsic object and the initial
+  value of the Symbol property of the global object.
+
+includes: [propertyHelper.js]
+---*/
+
+verifyNotEnumerable(this, "Symbol");
+verifyWritable(this, "Symbol");
+verifyConfigurable(this, "Symbol");