Flush InterfaceTypeImpl cached memebers when ClassElement.version is different.

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 456 matching lines @@
    */
   List<MethodElement> _methods;
 
   /**
    * A flag indicating whether the types associated with the instance members of
    * this class have been inferred.
    */
   bool _hasBeenInferred = false;
 
   /**
+   * The version of this element. The version is changed when the element is
+   * incrementally updated, so that its lists of constructors, accessors and
+   * methods might be different.
+   */
+  int version = 0;
+
+  /**
    * Initialize a newly created class element to have the given [name] at the
    * given [offset] in the file that contains the declaration of this element.
    */
   ClassElementImpl(String name, int offset)
       : _unlinkedClass = null,
         super(name, offset);
 
   /**
    * Initialize a newly created class element to have the given [name].
    */
@@ skipping 7991 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }