Make Map.keys/values Iterables.

sdk/lib/_internal/compiler/implementation/lib/constant_map.dart

Index: sdk/lib/_internal/compiler/implementation/lib/constant_map.dart
diff --git a/sdk/lib/_internal/compiler/implementation/lib/constant_map.dart b/sdk/lib/_internal/compiler/implementation/lib/constant_map.dart
index 4cb4049f1ba68e79e5a170cec4fdacf11d0cabcc..fabebbd9409216987699335fed2fef99fe1d1517 100644
--- a/sdk/lib/_internal/compiler/implementation/lib/constant_map.dart
+++ b/sdk/lib/_internal/compiler/implementation/lib/constant_map.dart
@@ -30,12 +30,12 @@ class ConstantMap<V> implements Map<String, V> {
     _keys.forEach((String key) => f(key, this[key]));
   }
 
-  Collection<String> get keys => _keys;
+  Iterable<String> get keys {
+    return new _ConstantMapKeyIterable(this);
+  }
 
-  Collection<V> get values {
-    List<V> result = <V>[];
-    _keys.forEach((String key) => result.add(this[key]));
-    return result;
+  Iterable<V> get values {
+    return new MappedIterable<String, V>(_keys, (String key) => this[key]);
   }
 
   bool get isEmpty => length == 0;
@@ -66,3 +66,10 @@ class ConstantProtoMap<V> extends ConstantMap<V> {
     return super[key];
   }
 }
+
+class _ConstantMapKeyIterable extends Iterable<String> {
+  ConstantMap _map;
+  _ConstantMapKeyIterable(this._map);
+
+  Iterator<String> get iterator => _map._keys.iterator;
+}