Handle use of constant constructors with default values.

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 1393 matching lines @@
     }
   }
 
   @override
   bool get isConst {
     _ensureConstant();
     return _isConst;
   }
 
   @override
+  bool get hasConstant => true;
+
+  @override
   ConstantExpression get constant {
     _ensureConstant();
     return _constant;
   }
 
   @override
   Expression get initializer => _unsupported('initializer');
 }
 
 class TopLevelFieldElementZ extends FieldElementZ with LibraryMemberMixin {
@@ skipping 427 matching lines @@
 
   ParameterElementZ(ObjectDecoder decoder) : super(decoder);
 
   @override
   bool get isFinal => _decoder.getBool(Key.IS_FINAL);
 
   @override
   bool get isConst => false;
 
   @override
+  bool get hasConstant => true;
+
+  @override
   ConstantExpression get constant {
     if (isOptional) {
       if (_constant == null) {
         _constant = _decoder.getConstant(Key.CONSTANT);
       }
       return _constant;
     }
     return null;
   }
 
@@ skipping 108 matching lines @@
   @override
   bool get isConst {
     if (_isConst == null) {
       _constant = _decoder.getConstant(Key.CONSTANT, isOptional: true);
       _isConst = _constant != null;
     }
     return _isConst;
   }
 
   @override
+  bool get hasConstant => true;
+
+  @override
   ConstantExpression get constant {
     if (isConst) {
       return _constant;
     }
     return null;
   }
 
   @override
   Expression get initializer => _unsupported('initializer');
 }
@@ skipping 128 matching lines @@
   }
 
   @override
   ElementKind get kind => ElementKind.PREFIX;
 
   @override
   Element lookupLocalMember(String memberName) {
     return _unsupported('lookupLocalMember');
   }
 }