All strong mode cleaning of dart2js.

pkg/compiler/lib/src/serialization/system.dart

Index: pkg/compiler/lib/src/serialization/system.dart
diff --git a/pkg/compiler/lib/src/serialization/system.dart b/pkg/compiler/lib/src/serialization/system.dart
index bed0dc0ee1868ad015828a35d6994ee1c69d1c55..8ae4efc0351ce9dfd306318b79cc05dfa646a15f 100644
--- a/pkg/compiler/lib/src/serialization/system.dart
+++ b/pkg/compiler/lib/src/serialization/system.dart
@@ -11,6 +11,7 @@ import '../common/resolution.dart';
 import '../compiler.dart';
 import '../elements/resolution_types.dart';
 import '../elements/elements.dart';
+import '../elements/entities.dart';
 import '../script.dart';
 import '../serialization/impact_serialization.dart';
 import 'package:front_end/src/fasta/scanner.dart';
@@ -108,7 +109,8 @@ class ResolutionDeserializerSystem extends DeserializerSystem {
   }
 
   @override
-  bool isDeserialized(Element element) {
+  bool isDeserialized(Entity entity) {
+    Element element = entity;
     return deserializedLibraries.contains(element.library);
   }
 }