Add ClassSet to support ClassWorld.strictSubtypesOf

pkg/compiler/lib/src/serialization/modelz.dart

 // Copyright (c) 2015, 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.
 
 /// Implementation of the element model used for deserialiation.
 ///
 /// These classes are created by [ElementDeserializer] triggered by the
 /// [Deserializer].
 
 library dart2js.serialization.modelz;
@@ skipping 922 matching lines @@
   }
 
   @override
   String get nativeTagInfo => _unsupported('nativeTagInfo');
 
   @override
   void reverseBackendMembers() => _unsupported('reverseBackendMembers');
 
   @override
   ClassElement get superclass => supertype != null ? supertype.element : null;
+
+  @override
+  void ensureResolved(Compiler compiler) {
+    compiler.world.registerClass(this);
+  }
 }
 
 abstract class ConstructorElementZ extends DeserializedElementZ
     with AnalyzableElementMixin,
          AstElementMixin,
          ClassMemberMixin,
          FunctionTypedElementMixin,
          ParametersMixin,
          TypedElementMixin,
          MemberElementMixin
@@ skipping 320 matching lines @@
   T get thisType {
     _ensureTypes();
     return _thisType;
   }
 
   @override
   T computeType(Compiler compiler) => thisType;
 
   @override
   bool get isResolved => true;
-
-  @override
-  void ensureResolved(Compiler compiler) {}
 }
 
 class TypedefElementZ extends DeserializedElementZ
     with AnalyzableElementMixin,
          AstElementMixin,
          LibraryMemberMixin,
          ParametersMixin,
          TypeDeclarationMixin<TypedefType>
     implements TypedefElement {
   DartType _alias;
@@ skipping 15 matching lines @@
 
   @override
   DartType get alias {
     if (_alias == null) {
       _alias = _decoder.getType(Key.ALIAS);
     }
     return _alias;
   }
 
   @override
+  void ensureResolved(Compiler compiler) {}
+
+  @override
   void checkCyclicReference(Compiler compiler) {}
 }
 
 class TypeVariableElementZ extends DeserializedElementZ
     with AnalyzableElementMixin,
          AstElementMixin,
          TypedElementMixin
     implements TypeVariableElement {
   TypeDeclarationElement _typeDeclaration;
   TypeVariableType _type;
@@ skipping 138 matching lines @@
 
   @override
   accept(ElementVisitor visitor, arg) {
     return visitor.visitFieldParameterElement(this, arg);
   }
 
   @override
   ElementKind get kind => ElementKind.INITIALIZING_FORMAL;
 
 }