Fail inference when an instance field is referenced.

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 7125 matching lines @@
           _unlinkedVariable.inferredTypeSlot, typeParameterContext);
       _declaredType = enclosingUnit.resynthesizerContext.resolveTypeRef(
           _unlinkedVariable.type, typeParameterContext,
           declaredType: true);
     }
     return super.type;
   }
 
   @override
   void set type(DartType type) {
+//    print('[type=] $type');
     _assertNotResynthesized(_unlinkedVariable);
     _type = type;
   }
 
   /**
    * Subclasses need this getter, see [ConstVariableElement._unlinkedConst].
    */
   UnlinkedExpr get _unlinkedConst => _unlinkedVariable?.initializer?.bodyExpr;
 }
 
@@ skipping 1724 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }