Create type masks lazily.

sdk/lib/_internal/compiler/implementation/elements/modelx.dart

 // Copyright (c) 2013, 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 elements.modelx;
 
 import 'dart:collection' show LinkedHashMap;
 
 import 'elements.dart';
 import '../../compiler.dart' as api;
@@ skipping 1492 matching lines @@
    * the input source has used explicit type arguments.
    *
    * This type is computed together with [thisType] in [computeType].
    */
   InterfaceType rawTypeCache;
   DartType supertype;
   Link<DartType> interfaces;
   SourceString nativeTagInfo;
   int supertypeLoadState;
   int resolutionState;
+  bool get isResolved => resolutionState == STATE_DONE;
 
   // backendMembers are members that have been added by the backend to simplify
   // compilation. They don't have any user-side counter-part.
   Link<Element> backendMembers = const Link<Element>();
 
   Link<DartType> allSupertypes;
 
   BaseClassElementX(SourceString name,
                     Element enclosing,
                     this.id,
@@ skipping 667 matching lines @@
 
   MetadataAnnotation ensureResolved(Compiler compiler) {
     if (resolutionState == STATE_NOT_STARTED) {
       compiler.resolver.resolveMetadataAnnotation(this);
     }
     return this;
   }
 
   String toString() => 'MetadataAnnotation($value, $resolutionState)';
 }