Introduce Substitution class and Supertype class.

lib/type_propagation/builder.dart

 // Copyright (c) 2016, 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 kernel.type_propagation.builder;
 
 import '../ast.dart';
 import '../class_hierarchy.dart';
 import '../core_types.dart';
 import 'canonicalizer.dart';
 import 'constraints.dart';
@@ skipping 157 matching lines @@
     // subtype information.
     for (int i = 0; i < hierarchy.classes.length; ++i) {
       Class class_ = hierarchy.classes[i];
       List<int> supers = <int>[];
       if (class_.supertype != null) {
         supers.add(getLatticePointForSubtypesOfClass(class_.superclass));
       }
       if (class_.mixedInType != null) {
         supers.add(getLatticePointForSubtypesOfClass(class_.mixedInClass));
       }
-      for (InterfaceType supertype in class_.implementedTypes) {
+      for (Supertype supertype in class_.implementedTypes) {
         supers.add(getLatticePointForSubtypesOfClass(supertype.classNode));
       }
       int subtypePoint = newLatticePoint(supers, class_,
           i == 0 ? BaseClassKind.Subclass : BaseClassKind.Subtype);
       lattice.subtypesOfClass[i] = subtypePoint;
       visualizer?.annotateLatticePoint(subtypePoint, class_, 'subtype');
     }
 
     // Build the lattice points for subclasses and exact classes.
     for (int i = 0; i < hierarchy.classes.length; ++i) {
@@ skipping 1783 matching lines @@
         environment.addStore(input, field, argument);
       }
     }
     for (int arity = minArity; arity <= maxArity; ++arity) {
       int returnLocation =
           environment.getLoad(input, fieldNames.getReturnField(arity));
       visitContravariant(node.returnType, returnLocation);
     }
   }
 }