Add tests to verify valid object shorthand properties

Fixes #1202

test/language/expressions/object/identifier-shorthand-invalid-computed-name.js

+// Copyright (C) 2017 The V8 Project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+  Object literal shorthands are only valid with identifier references,
+  not computed property names.
+esid: sec-object-initializer
+info: |
+  PropertyDefinition:
+    IdentifierReference
+    CoverInitializedName
+    PropertyName : AssignmentExpression
+    MethodDefinition
+
+  PropertyName:
+    LiteralPropertyName
+    ComputedPropertyName
+negative:
+  phase: early
+  type: SyntaxError
+---*/
+
+var x = "y";
+var y = 42;
+
+throw "Test262: This statement should not be evaluated.";
+
+({[x]});

test/language/expressions/object/identifier-shorthand-invalid-zero.js

+// Copyright (C) 2017 The V8 Project authors. All rights reserved.
+// This code is governed by the BSD license found in the LICENSE file.
+
+/*---
+description: >
+  Object literal shorthands are only valid with identifier references,
+  not property names. (0)
+esid: sec-object-initializer
+info: |
+  PropertyDefinition:
+    IdentifierReference
+    CoverInitializedName
+    PropertyName : AssignmentExpression
+    MethodDefinition
+negative:
+  phase: early
+  type: SyntaxError
+---*/
+
+throw "Test262: This statement should not be evaluated.";
+
+({0});