Handle redirecting factories.

tests/compiler/dart2js/serialization/test_data.dart

Index: tests/compiler/dart2js/serialization/test_data.dart
diff --git a/tests/compiler/dart2js/serialization/test_data.dart b/tests/compiler/dart2js/serialization/test_data.dart
index 0606a48621cbd6c1e66c4db5b92a11e21238d2d1..6eb7d72fa1f6ad01a39552d3646cfa35e6edd254 100644
--- a/tests/compiler/dart2js/serialization/test_data.dart
+++ b/tests/compiler/dart2js/serialization/test_data.dart
@@ -217,6 +217,22 @@ class C {
 }
 main() => const C();'''
   }),
+
+  const Test(const {
+    'main.dart': '''
+class C {
+  factory C() = Object;
+}
+main() => new C();'''
+  }),
+
+  const Test(const {
+    'main.dart': '''
+abstract class C implements List {
+  factory C([_]) = List;
+}
+main() => new C();'''
+  }),
 ];
 
 class Test {