Introduce LibraryEntity

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

Index: pkg/compiler/lib/src/serialization/serialization_util.dart
diff --git a/pkg/compiler/lib/src/serialization/serialization_util.dart b/pkg/compiler/lib/src/serialization/serialization_util.dart
index 8d60881c3061ded30f10685f0576e6fdc2d6d776..9c7d1a818a17072241ef8b661ce05bdd8f6d2c71 100644
--- a/pkg/compiler/lib/src/serialization/serialization_util.dart
+++ b/pkg/compiler/lib/src/serialization/serialization_util.dart
@@ -23,7 +23,8 @@ void serializeName(Name name, ObjectEncoder encoder) {
   encoder.setString(Key.NAME, name.text);
   encoder.setBool(Key.IS_SETTER, name.isSetter);
   if (name.library != null) {
-    encoder.setElement(Key.LIBRARY, name.library);
+    LibraryElement library = name.library;
+    encoder.setElement(Key.LIBRARY, library);
   }
 }