Implement least upper bound.

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 'elements.dart';
 import '../../compiler.dart' as api;
 import '../tree/tree.dart';
 import '../util/util.dart';
@@ skipping 11 matching lines @@
                                  FunctionType,
                                  Selector,
                                  Constant,
                                  Compiler,
                                  isPrivateName;
 
 import '../dart_types.dart';
 
 import '../scanner/scannerlib.dart' show Token, EOF_TOKEN;
 
+import '../ordered_typeset.dart' show OrderedTypeSet;
+
 
 class ElementX implements Element {
   static int elementHashCode = 0;
 
   final String name;
   final ElementKind kind;
   final Element enclosingElement;
   final int hashCode = ++elementHashCode;
   Link<MetadataAnnotation> metadata = const Link<MetadataAnnotation>();
 
@@ skipping 1645 matching lines @@
   Link<DartType> interfaces;
   String 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;
+  OrderedTypeSet allSupertypesAndSelf;
+
+  Link<DartType> get allSupertypes => allSupertypesAndSelf.supertypes;
+
+  int get hierarchyDepth => allSupertypesAndSelf.maxDepth;
 
   BaseClassElementX(String name,
                     Element enclosing,
                     this.id,
                     int initialState)
       : supertypeLoadState = initialState,
         resolutionState = initialState,
         super(name, ElementKind.CLASS, enclosing);
 
   int get hashCode => id;
@@ skipping 662 matching lines @@
 
   MetadataAnnotation ensureResolved(Compiler compiler) {
     if (resolutionState == STATE_NOT_STARTED) {
       compiler.resolver.resolveMetadataAnnotation(this);
     }
     return this;
   }
 
   String toString() => 'MetadataAnnotation($value, $resolutionState)';
 }