Remove usage of dart:json.

pkg/serialization/test/serialization_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 serialization_test;
 
-import 'dart:json' as json;
+import 'dart:convert';
 import 'package:unittest/unittest.dart';
 import 'package:serialization/serialization.dart';
 import 'package:serialization/src/serialization_helpers.dart';
 import 'package:serialization/src/mirrors_helpers.dart';
 import 'dart:isolate';
 
 part 'test_models.dart';
 
 void main() {
   var p1 = new Person();
@@ skipping 341 matching lines @@
     var newAddress = s.read(out);
     expect(newAddress.street, a1.street);
     expect(newAddress.city, "Kirkland");
     expect(newAddress.state, "WA");
     expect(newAddress.zip, "98103");
   });
 
   test("Straight JSON format", () {
     var s = new Serialization();
     var writer = s.newWriter(const SimpleJsonFormat());
-    var out = json.stringify(writer.write(a1));
-    var reconstituted = json.parse(out);
+    var out = JSON.encode(writer.write(a1));
+    var reconstituted = JSON.decode(out);
     expect(reconstituted.length, 4);
     expect(reconstituted[0], "Seattle");
   });
 
   test("Straight JSON format, nested objects", () {
     var p1 = new Person()..name = 'Alice'..address = a1;
     var s = new Serialization()..selfDescribing = false;
     var addressRule = s.addRuleFor(Address)..configureForMaps();
     var personRule = s.addRuleFor(Person)..configureForMaps();
     var writer = s.newWriter(const SimpleJsonFormat(storeRoundTripInfo: true));
-    var out = json.stringify(writer.write(p1));
-    var reconstituted = json.parse(out);
+    var out = JSON.encode(writer.write(p1));
+    var reconstituted = JSON.decode(out);
     var expected = {
       "name" : "Alice",
       "rank" : null,
       "serialNumber" : null,
       "_rule" : personRule.number,
       "address" : {
         "street" : "N 34th",
         "city" : "Seattle",
         "state" : null,
         "zip" : null,
@@ skipping 413 matching lines @@
 
 /**
  * Function used in an isolate to make sure that the output passes through
  * isolate serialization properly.
  */
 void echo() {
   port.receive((msg, reply) {
     reply.send(msg);
   });
 }