Don't prevent 'isCycleFree' updating for resynthesized constructors.

pkg/analyzer/lib/src/dart/element/element.dart

 // Copyright (c) 2014, 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 analyzer.src.dart.element.element;
 
 import 'dart:collection';
 import 'dart:math' show min;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 2053 matching lines @@
   bool get isCycleFree {
     if (serializedExecutable != null) {
       return serializedExecutable.isConst &&
           !enclosingUnit.resynthesizerContext
               .isInConstCycle(serializedExecutable.constCycleSlot);
     }
     return _isCycleFree;
   }
 
   void set isCycleFree(bool isCycleFree) {
-    assert(serializedExecutable == null);
     _isCycleFree = isCycleFree;
   }
 
   @override
   bool get isDefaultConstructor {
     // unnamed
     String name = this.name;
     if (name != null && name.length != 0) {
       return false;
     }
@@ skipping 6355 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }