Make mappedBy lazy.

pkg/intl/test/date_time_format_test_core.dart

Index: pkg/intl/test/date_time_format_test_core.dart
diff --git a/pkg/intl/test/date_time_format_test_core.dart b/pkg/intl/test/date_time_format_test_core.dart
index c2d502145b181ed249614e33dfddc6a4408dfcd9..4e92fb648235c887c84b19525702086080e52a50 100644
--- a/pkg/intl/test/date_time_format_test_core.dart
+++ b/pkg/intl/test/date_time_format_test_core.dart
@@ -217,10 +217,14 @@ runDateTests([List<String> subset]) {
   test('Basic date format parsing', () {
     var date_format = new DateFormat("d");
     expect(
-        date_format.parsePattern("hh:mm:ss").mappedBy((x) => x.pattern),
+        date_format.parsePattern("hh:mm:ss")
+            .mappedBy((x) => x.pattern)
+            .toList(),
         orderedEquals(["hh",":", "mm",":","ss"]));
     expect(
-        date_format.parsePattern("hh:mm:ss").mappedBy((x) => x.pattern),
+        date_format.parsePattern("hh:mm:ss")
+            .mappedBy((x) => x.pattern)
+            .toList(),
         orderedEquals(["hh",":", "mm",":","ss"]));
   });