Fix factories in Frog to correspond to the new syntax.

corelib/src/time_zone.dart

Index: corelib/src/time_zone.dart
diff --git a/corelib/src/time_zone.dart b/corelib/src/time_zone.dart
index a4676e7a2787f92b41509f41e4ba7be101d9280a..89f6cc59170b39a1778586838b5b1e5bf14aec59 100644
--- a/corelib/src/time_zone.dart
+++ b/corelib/src/time_zone.dart
@@ -7,7 +7,7 @@
 /**
  * [TimeZone]s represent locations (for example Europe/Paris).
  */
-interface TimeZone factory TimeZoneImplementation {
+interface TimeZone default TimeZoneImplementation {
   const TimeZone.utc();
   TimeZone.local();
   bool get isUtc();