Fix JSON encoder accepting NaN and Infinity.

tests/lib/convert/json_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library json_test;
 
 import "package:expect/expect.dart";
 import "dart:convert";
 
 bool badFormat(e) => e is FormatException;
@@ skipping 117 matching lines @@
   // No whitespace inside numbers.
   // Additional case "- 2.2e+2" in json_strict_test.dart.
   testThrows("-2 .2e+2");
   testThrows("-2. 2e+2");
   testThrows("-2.2 e+2");
   testThrows("-2.2e +2");
   testThrows("-2.2e+ 2");
 
   testThrows("[2.,2]");
   testThrows("{2.:2}");
+
+  testThrows("NaN");
+  testThrows("Infinity");
+  testThrows("-Infinity");
+  Expect.throws(() => JSON.encode(double.NAN));
+  Expect.throws(() => JSON.encode(double.INFINITY));
+  Expect.throws(() => JSON.encode(double.NEGATIVE_INFINITY));
 }
 
 testStrings() {
   // String parser accepts and understands escapes.
   var input = r'"\u0000\uffff\n\r\f\t\b\/\\\"' '\x20\ufffd\uffff"';
   var expected = "\u0000\uffff\n\r\f\t\b\/\\\"\x20\ufffd\uffff";
   testJson(input, expected);
   // Empty string.
   testJson(r'""', "");
   // Escape first.
@@ skipping 112 matching lines @@
 }
 
 main() {
   testNumbers();
   testStrings();
   testWords();
   testObjects();
   testArrays();
   testWhitespace();
 }