Extract ReceiverMask interface from TypeMask.

pkg/compiler/lib/src/enqueue.dart

Index: pkg/compiler/lib/src/enqueue.dart
diff --git a/pkg/compiler/lib/src/enqueue.dart b/pkg/compiler/lib/src/enqueue.dart
index 2656ee92da30b2c4307f4e26263651b53f1c1f49..6ad51775b4ac6b19960671dd5d468bf98ac0e970 100644
--- a/pkg/compiler/lib/src/enqueue.dart
+++ b/pkg/compiler/lib/src/enqueue.dart
@@ -53,6 +53,8 @@ import 'resolution/members.dart' show
     ResolverVisitor;
 import 'tree/tree.dart' show
     Send;
+import 'types/types.dart' show
+    TypeMaskStrategy;
 import 'universe/universe.dart';
 import 'util/util.dart' show
     Link,
@@ -122,7 +124,7 @@ abstract class Enqueuer {
       = new Map<String, Set<Element>>();
   final Set<ClassElement> _processedClasses = new Set<ClassElement>();
   Set<ClassElement> recentClasses = new Setlet<ClassElement>();
-  final Universe universe = new Universe();
+  final Universe universe = new Universe(const TypeMaskStrategy());
 
   static final TRACE_MIRROR_ENQUEUING =
       const bool.fromEnvironment("TRACE_MIRROR_ENQUEUING");