Extract DartTypeVisitor and subclasses from resolution_types.

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

Index: pkg/compiler/lib/src/serialization/type_serialization.dart
diff --git a/pkg/compiler/lib/src/serialization/type_serialization.dart b/pkg/compiler/lib/src/serialization/type_serialization.dart
index 89ab51055155832c8f7924e3baa928508f9a2da6..5702f3bcf2f11bdf8dc31aa2a4b2a2e43037a487 100644
--- a/pkg/compiler/lib/src/serialization/type_serialization.dart
+++ b/pkg/compiler/lib/src/serialization/type_serialization.dart
@@ -16,7 +16,7 @@ import 'serialization.dart';
 /// serialization. The [ObjectEncoder] ensures that any [Element], and other
 /// [ResolutionDartType] that the serialized [ResolutionDartType] depends upon
 /// are also serialized.
-class TypeSerializer extends DartTypeVisitor<dynamic, ObjectEncoder> {
+class TypeSerializer extends ResolutionDartTypeVisitor<dynamic, ObjectEncoder> {
   const TypeSerializer();
 
   void visitType(ResolutionDartType type, ObjectEncoder encoder) {