Don't serialize unnamed mixin applications.

tests/compiler/dart2js/serialization_test.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart2js.serialization_test;
 
 import 'dart:io';
 import 'memory_compiler.dart';
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/constants/constructors.dart';
@@ skipping 530 matching lines @@
     }
     for (Element member in members2) {
       names.add(member.name);
     }
     element1 = element1.implementation;
     element2 = element2.implementation;
     for (String name in names) {
       Element member1 = element1.localLookup(name);
       Element member2 = element2.localLookup(name);
       if (member1 == null) {
-        print('Missing member for $member2 in\n ${members1.join('\n ')}');
-        continue;
+        String message =
+            'Missing member for $member2 in\n ${members1.join('\n ')}';
+        if (member2.isAbstractField) {
+          // TODO(johnniwinther): Ensure abstract fields are handled correctly.
+          print(message);
+          continue;
+        } else {
+          throw message;
+        }
       }
       if (member2 == null) {
-        print('Missing member for $member1 in\n ${members2.join('\n ')}');
-        continue;
+        String message =
+            'Missing member for $member1 in\n ${members2.join('\n ')}';
+        if (member1.isAbstractField) {
+          // TODO(johnniwinther): Ensure abstract fields are handled correctly.
+          print(message);
+          continue;
+        } else {
+          throw message;
+        }
       }
       visit(member1, member2);
     }
   }
 
   @override
   void visitClassElement(ClassElement element1, ClassElement element2) {
     checkElementIdentities(null, null, null, element1, element2);
     check(element1, element2, 'name',
           element1.name, element2.name);
@@ skipping 47 matching lines @@
     checkTypeLists(
         element1, element2, 'types',
         typeSet1.types.toList(),
         typeSet2.types.toList());
 
     checkTypeLists(
         element1, element2, 'interfaces',
         element1.interfaces.toList(),
         element2.interfaces.toList());
 
+    List<ConstructorElement> getConstructors(ClassElement cls) {
+      return cls.implementation.constructors.map((c) => c.declaration).toList();
+    }
+
+    checkElementLists(
+        element1, element2, 'constructors',
+        getConstructors(element1),
+        getConstructors(element2));
+
     visitMembers(element1, element2);
   }
 
   @override
   void visitFieldElement(FieldElement element1, FieldElement element2) {
     checkElementIdentities(null, null, null, element1, element2);
     check(element1, element2, 'name',
           element1.name, element2.name);
     check(element1, element2, 'sourcePosition',
           element1.sourcePosition, element2.sourcePosition);
@@ skipping 466 matching lines @@
         exp1, exp2, 'expression',
         exp1.expression, exp2.expression);
   }
 
   @override
   visitDeferred(DeferredConstantExpression exp1,
                 DeferredConstantExpression exp2) {
     // TODO: implement visitDeferred
   }
 }