Resynthesize FieldFormalParameterElementImpl(s) lazily.

pkg/analyzer/lib/src/dart/element/builder.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.builder;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 1285 matching lines @@
    * Build the table mapping field names to field elements for the fields defined in the current
    * class.
    *
    * @param fields the field elements defined in the current class
    */
   void _buildFieldMap(List<FieldElement> fields) {
     _fieldMap = new HashMap<String, FieldElement>();
     int count = fields.length;
     for (int i = 0; i < count; i++) {
       FieldElement field = fields[i];
-      _fieldMap[field.name] = field;
+      _fieldMap[field.name] ??= field;

[Brian Wilkerson, 2016/05/25 23:14:49]

Inline field to avoid a list access when not necessary?

     }
   }
 
   /**
    * Creates the [ConstructorElement]s array with the single default constructor element.
    *
    * @param interfaceType the interface type for which to create a default constructor
    * @return the [ConstructorElement]s array with the single default constructor element
    */
   List<ConstructorElement> _createDefaultConstructors(
@@ skipping 189 matching lines @@
     return null;
   }
 
   /**
    * Return the lexical identifiers associated with the given [identifiers].
    */
   static List<String> _getIdentifiers(NodeList<SimpleIdentifier> identifiers) {
     return identifiers.map((identifier) => identifier.name).toList();
   }
 }