Handle forwarding constructors

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 d27ec305fd72e4bae5aea5c7d3cbd4fc2b4b0031..2937d5b41210b73ca144037ddaac3d53e2b9a861 100644
--- a/tests/compiler/dart2js/serialization/test_data.dart
+++ b/tests/compiler/dart2js/serialization/test_data.dart
@@ -466,6 +466,21 @@ main() => m(null, null, null);
 m(a, b, c) => a[b] ??= c;
 ''',
   }),
+
+  const Test('Forwarding constructor defined by forwarding constructor', const {
+    'main.dart': '''
+import 'a.dart';
+
+main() => new C();
+''',
+  }, preserializedSourceFiles: const {
+    'a.dart': '''
+class A {}
+class B {}
+class C {}
+class D = A with B, C;
+''',
+  }),
 ];
 
 class Test {