Use JsonMap even for JSON.decode with custom reviver.

tests/corelib/json_map_test.dart

Index: tests/corelib/json_map_test.dart
diff --git a/tests/corelib/json_map_test.dart b/tests/corelib/json_map_test.dart
index faffb7c9304406c9d81c4616c1db9307390e2d5a..21dcdb02492ff4131dfe445351848cacc6df64ec 100644
--- a/tests/corelib/json_map_test.dart
+++ b/tests/corelib/json_map_test.dart
@@ -8,7 +8,13 @@ import "package:expect/expect.dart";
 import 'dart:convert' show JSON;
 import 'dart:collection' show LinkedHashMap, HashMap;
 
-Map jsonify(Map map) => JSON.decode(JSON.encode(map));
+bool useReviver = false;
+Map jsonify(Map map) {
+  String encoded = JSON.encode(map);
+  return useReviver
+      ? JSON.decode(encoded, reviver: (key, value) => value)
+      : JSON.decode(encoded);
+}
 
 List listEach(Map map) {
   var result = [];
@@ -20,6 +26,12 @@ List listEach(Map map) {
 }
 
 void main() {
+  test(false);
+  test(true);
+}
+
+void test(bool revive) {
+  useReviver = revive;
   testEmpty(jsonify({}));
   testAtoB(jsonify({'a': 'b'}));