Don't resolve FieldFormalParameter field if not in constructor.

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 4296 matching lines @@
   /**
    * Initialize using the given serialized information.
    */
   FieldFormalParameterElementImpl.forSerialized(
       UnlinkedParam unlinkedParam, ElementImpl enclosingElement)
       : super.forSerialized(unlinkedParam, enclosingElement);
 
   @override
   FieldElement get field {
     if (_unlinkedParam != null && _field == null) {
-      Element enclosing = enclosingElement?.enclosingElement;
-      while (enclosing != null) {
-        if (enclosing is ClassElement) {
-          _field = enclosing.getField(_unlinkedParam.name);
-          break;
-        } else {
-          enclosing = enclosing.enclosingElement;
+      Element enclosingConstructor = enclosingElement;
+      if (enclosingConstructor is ConstructorElement) {
+        Element enclosingClass = enclosingConstructor.enclosingElement;
+        if (enclosingClass is ClassElement) {
+          FieldElement field = enclosingClass.getField(_unlinkedParam.name);
+          if (field != null && !field.isSynthetic) {
+            _field = field;
+          }
         }
       }
     }
     return _field;
   }
 
   void set field(FieldElement field) {
     _assertNotResynthesized(_unlinkedParam);
     _field = field;
   }
@@ skipping 4304 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }