Make the JSON decoder (parser) create Dart maps lazily

tests/corelib/map_test.dart

 // Copyright (c) 2011, 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 map_test;
 import "package:expect/expect.dart";
 import 'dart:collection';
+import 'dart:convert' show JSON;
+
+Map newJsonMap() => JSON.decode('{}');
 
 void main() {
   test(new HashMap());
   test(new LinkedHashMap());
   test(new SplayTreeMap());
   test(new SplayTreeMap(Comparable.compare));
   test(new MapView(new HashMap()));
   test(new MapView(new SplayTreeMap()));
   test(new MapBaseMap());
   test(new MapMixinMap());
+  test(newJsonMap());
   testLinkedHashMap();
   testMapLiteral();
   testNullValue();
   testTypes();
 
   testWeirdStringKeys(new Map());
   testWeirdStringKeys(new Map<String, String>());
   testWeirdStringKeys(new HashMap());
   testWeirdStringKeys(new HashMap<String, String>());
   testWeirdStringKeys(new LinkedHashMap());
   testWeirdStringKeys(new LinkedHashMap<String, String>());
   testWeirdStringKeys(new SplayTreeMap());
   testWeirdStringKeys(new SplayTreeMap<String, String>());
   testWeirdStringKeys(new MapBaseMap<String, String>());
   testWeirdStringKeys(new MapMixinMap<String, String>());
+  testWeirdStringKeys(newJsonMap());
 
   testNumericKeys(new Map());
   testNumericKeys(new Map<num, String>());
   testNumericKeys(new HashMap());
   testNumericKeys(new HashMap<num, String>());
   testNumericKeys(new HashMap.identity());
   testNumericKeys(new HashMap<num, String>.identity());
   testNumericKeys(new LinkedHashMap());
   testNumericKeys(new LinkedHashMap<num, String>());
   testNumericKeys(new LinkedHashMap.identity());
   testNumericKeys(new LinkedHashMap<num, String>.identity());
   testNumericKeys(new MapBaseMap<num, String>());
   testNumericKeys(new MapMixinMap<num, String>());
+  testNumericKeys(newJsonMap());
 
   testNaNKeys(new Map());
   testNaNKeys(new Map<num, String>());
   testNaNKeys(new HashMap());
   testNaNKeys(new HashMap<num, String>());
   testNaNKeys(new LinkedHashMap());
   testNaNKeys(new LinkedHashMap<num, String>());
   testNaNKeys(new MapBaseMap<num, String>());
   testNaNKeys(new MapMixinMap<num, String>());
+  testNaNKeys(newJsonMap());
   // Identity maps fail the NaN-keys tests because the test assumes that
   // NaN is not equal to NaN.
 
   testIdentityMap(new Map.identity());
   testIdentityMap(new HashMap.identity());
   testIdentityMap(new LinkedHashMap.identity());
   testIdentityMap(new HashMap(equals: identical,
                               hashCode: identityHashCode));
   testIdentityMap(new LinkedHashMap(equals: identical,
                                     hashCode: identityHashCode));
   testIdentityMap(new HashMap(equals: (x, y) => identical(x, y),
                               hashCode: (x) => identityHashCode(x)));
   testIdentityMap(new LinkedHashMap(equals: (x, y) => identical(x, y),
                                     hashCode: (x) => identityHashCode(x)));
 
   testCustomMap(new HashMap(equals: myEquals, hashCode: myHashCode,
                             isValidKey: (v) => v is Customer));
   testCustomMap(new LinkedHashMap(equals: myEquals, hashCode: myHashCode,
                                   isValidKey: (v) => v is Customer));
   testCustomMap(new HashMap<Customer,dynamic>(equals: myEquals,
                                               hashCode: myHashCode));
 
   testCustomMap(new LinkedHashMap<Customer,dynamic>(equals: myEquals,
                                                     hashCode: myHashCode));
 
   testIterationOrder(new LinkedHashMap());
   testIterationOrder(new LinkedHashMap.identity());
+  testIterationOrder(newJsonMap());
 
   testOtherKeys(new SplayTreeMap<int, int>());
   testOtherKeys(new SplayTreeMap<int, int>((int a, int b) => a - b,
                                            (v) => v is int));
   testOtherKeys(new SplayTreeMap((int a, int b) => a - b,
                                  (v) => v is int));
   testOtherKeys(new HashMap<int, int>());
   testOtherKeys(new HashMap<int, int>.identity());
   testOtherKeys(new HashMap<int, int>(hashCode: (v) => v.hashCode,
                                       isValidKey: (v) => v is int));
   testOtherKeys(new HashMap(equals: (int x, int y) => x == y,
                             hashCode: (int v) => v.hashCode,
                             isValidKey: (v) => v is int));
   testOtherKeys(new LinkedHashMap<int, int>());
   testOtherKeys(new LinkedHashMap<int, int>.identity());
   testOtherKeys(new LinkedHashMap<int, int>(hashCode: (v) => v.hashCode,
                                        isValidKey: (v) => v is int));
   testOtherKeys(new LinkedHashMap(equals: (int x, int y) => x == y,
                                   hashCode: (int v) => v.hashCode,
                                   isValidKey: (v) => v is int));
   testOtherKeys(new MapBaseMap<int, int>());
   testOtherKeys(new MapMixinMap<int, int>());
+  testOtherKeys(newJsonMap());
 
   testUnmodifiableMap(const {1 : 37});
   testUnmodifiableMap(new UnmodifiableMapView({1 : 37}));
   testUnmodifiableMap(new UnmodifiableMapBaseMap([1, 37]));
 }
 
 
 void test(Map map) {
   testDeletedElement(map);
   testMap(map, 1, 2, 3, 4, 5, 6, 7, 8);
@@ skipping 759 matching lines @@
   int get _modCount => 0;
 
   V operator[](K key) {
     int index = _keys.indexOf(key);
     if (index < 0) return null;
     return _values[index];
   }
 
   Iterable<K> get keys => _keys.skip(0);
 }