Serialize default constructors separately.

pkg/compiler/lib/src/serialization/modelz.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.
 
 /// Implementation of the element model used for deserialiation.
 ///
 /// These classes are created by [ElementDeserializer] triggered by the
 /// [Deserializer].
 
 library dart2js.serialization.modelz;
@@ skipping 1072 matching lines @@
       }
       _constantConstructor = ConstantConstructorDeserializer.deserialize(data);
     }
     return _constantConstructor;
   }
 
   @override
   AsyncMarker get asyncMarker => AsyncMarker.SYNC;
 
   @override
-  ConstructorElement get definingConstructor {
-    String name =
-        _decoder.getString(Key.DEFINING_CONSTRUCTOR, isOptional: true);
-    if (name != null) {
-      return enclosingClass.superclass.lookupConstructor(name);
-    }
-    return null;
-  }
+  ConstructorElement get definingConstructor => null;
 
   @override
   ConstructorElement get effectiveTarget {
     if (_effectiveTarget == null) {
       _effectiveTarget =
           _decoder.getElement(Key.EFFECTIVE_TARGET, isOptional: true);
       if (_effectiveTarget == null) {
         _effectiveTarget = this;
       }
     }
@@ skipping 25 matching lines @@
 }
 
 class GenerativeConstructorElementZ extends ConstructorElementZ {
   GenerativeConstructorElementZ(ObjectDecoder decoder) : super(decoder);
 
   @override
   ElementKind get kind => ElementKind.GENERATIVE_CONSTRUCTOR;
 
   @override
   bool get isRedirectingGenerative => _decoder.getBool(Key.IS_REDIRECTING);
+}
+
+class DefaultConstructorElementZ extends ConstructorElementZ {
+  DefaultConstructorElementZ(ObjectDecoder decoder) : super(decoder);
 
   @override
-  bool get isSynthesized => definingConstructor != null;
+  ElementKind get kind => ElementKind.GENERATIVE_CONSTRUCTOR;
+
+  @override
+  bool get isSynthesized => true;
+
+  @override
+  ConstructorElement get definingConstructor {
+    return enclosingClass.superclass.lookupConstructor('');
+  }
 }
 
 class FactoryConstructorElementZ extends ConstructorElementZ {
   FactoryConstructorElementZ(ObjectDecoder decoder) : super(decoder);
 
   @override
   ElementKind get kind => ElementKind.FACTORY_CONSTRUCTOR;
 }
 
 class RedirectingFactoryConstructorElementZ extends ConstructorElementZ {
@@ skipping 921 matching lines @@
   }
 
   @override
   ElementKind get kind => ElementKind.PREFIX;
 
   @override
   Element lookupLocalMember(String memberName) {
     return _unsupported('lookupLocalMember');
   }
 }