Use elements/types.dart in codegen.dart

pkg/compiler/lib/src/elements/resolution_types.dart

Index: pkg/compiler/lib/src/elements/resolution_types.dart
diff --git a/pkg/compiler/lib/src/elements/resolution_types.dart b/pkg/compiler/lib/src/elements/resolution_types.dart
index 785a27193d494b1d356ca392d10daa3bac10c642..8168305002430977a8f442fe3f88514389adf392 100644
--- a/pkg/compiler/lib/src/elements/resolution_types.dart
+++ b/pkg/compiler/lib/src/elements/resolution_types.dart
@@ -356,7 +356,7 @@ class MalformedType extends DartType {
   }
 }
 
-abstract class GenericType extends DartType {
+abstract class GenericType<T extends GenericType> extends DartType {
   final TypeDeclarationElement element;
   final List<DartType> typeArguments;
 
@@ -381,9 +381,9 @@ abstract class GenericType extends DartType {
   }
 
   /// Creates a new instance of this type using the provided type arguments.
-  GenericType createInstantiation(List<DartType> newTypeArguments);
+  T createInstantiation(List<DartType> newTypeArguments);
 
-  DartType subst(List<DartType> arguments, List<DartType> parameters) {
+  T subst(List<DartType> arguments, List<DartType> parameters) {
     if (typeArguments.isEmpty) {
       // Return fast on non-generic types.
       return this;
@@ -471,7 +471,8 @@ abstract class GenericType extends DartType {
   }
 }
 
-class InterfaceType extends GenericType implements types.InterfaceType {
+class InterfaceType extends GenericType<InterfaceType>
+    implements types.InterfaceType {
   int _hashCode;
 
   InterfaceType(ClassElement element,
@@ -809,7 +810,7 @@ class FunctionType extends DartType implements types.FunctionType {
 bool _typeContainsMethodTypeVariableType(DartType type) =>
     type.containsMethodTypeVariableType;
 
-class TypedefType extends GenericType {
+class TypedefType extends GenericType<TypedefType> {
   DartType _unaliased;
 
   TypedefType(TypedefElement element,