Resynthesize _DeferredClassElement instead of actual ClassElementImpl.

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 1064 matching lines @@
   }
 
   @override
   List<ClassElement> get types => _types;
 
   /**
    * Set the types contained in this compilation unit to the given [types].
    */
   void set types(List<ClassElement> types) {
     for (ClassElement type in types) {
-      (type as ClassElementImpl).enclosingElement = this;
+      if (type is ClassElementImpl) {

[Paul Berry, 2016/03/24 19:40:14]

Nit: it's not obvious without reading the rest of the CL why this change is
necessary, which makes me worry that when someone comes back to maintain this
code later they'll be confused.

Consider changing to "if (type is! DeferredClassElement)"

so that if someone comes across this code later they can just navigate to
DeferredClassElement and figure out what is going on.

+        type.enclosingElement = this;
+      }
     }
     this._types = types;
   }
 
   @override
   bool operator ==(Object object) =>
       object is CompilationUnitElementImpl && source == object.source;
 
   @override
   accept(ElementVisitor visitor) => visitor.visitCompilationUnitElement(this);
@@ skipping 3848 matching lines @@
 
   @override
   void visitElement(Element element) {
     int offset = element.nameOffset;
     if (offset != -1) {
       map[offset] = element;
     }
     super.visitElement(element);
   }
 }