Cast InternalMap to Map.

pkg/dev_compiler/tool/input_sdk/private/isolate_serialization.dart

Index: pkg/dev_compiler/tool/input_sdk/private/isolate_serialization.dart
diff --git a/pkg/dev_compiler/tool/input_sdk/private/isolate_serialization.dart b/pkg/dev_compiler/tool/input_sdk/private/isolate_serialization.dart
index 741cc2aacfadbddb994e9c35bb99e51cb49f0b13..28c03f801d486b4342a759857bedfe91c51c66e1 100644
--- a/pkg/dev_compiler/tool/input_sdk/private/isolate_serialization.dart
+++ b/pkg/dev_compiler/tool/input_sdk/private/isolate_serialization.dart
@@ -114,7 +114,7 @@ class _Serializer {
     return x;
   }
 
-  serializeMap(Map x) {
+  serializeMap(InternalMap x) {
     Function serializeTearOff = serialize;
     return ['map',
             x.keys.map(serializeTearOff).toList(),
@@ -276,7 +276,7 @@ class _Deserializer {
   }
 
   // ['map', <key-list>, <value-list>].
-  Map deserializeMap(x) {
+  Map deserializeMap(InternalMap x) {
     assert(x[0] == 'map');
     List keys = x[1];
     List values = x[2];