Test for changing method to/from getter/setter.

pkg/analyzer/lib/src/generated/incremental_resolver.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.generated.incremental_resolver;
 
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'package:analyzer/dart/element/element.dart';
@@ skipping 339 matching lines @@
       _removedElements.remove(element);
       // matches, update the existing element
       node.name.staticElement = element;
       _setLocalElements(element, newElement);
     } on _DeclarationMismatchException {
       _removeElement(element);
       // add new element
       if (newElement != null) {
         _addedElements.add(newElement);
         if (newElement is MethodElement) {
-          List<MethodElement> methods = _enclosingClass.methods;
+          List<MethodElement> methods = _enclosingClass.methods.toList();
           methods.add(newElement);
           _enclosingClass.methods = methods;
         } else {
-          List<PropertyAccessorElement> accessors = _enclosingClass.accessors;
+          List<PropertyAccessorElement> accessors =
+              _enclosingClass.accessors.toList();
           accessors.add(newElement);
           _enclosingClass.accessors = accessors;
         }
       }
     }
   }
 
   @override
   visitPartDirective(PartDirective node) {
     String uri = _getStringValue(node.uri);
@@ skipping 1721 matching lines @@
   @override
   String toString() => name;
 }
 
 class _TokenPair {
   final _TokenDifferenceKind kind;
   final Token oldToken;
   final Token newToken;
   _TokenPair(this.kind, this.oldToken, this.newToken);
 }