Extract DartTypeVisitor and subclasses from resolution_types.

tests/compiler/dart2js/related_types.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.
 
 library related_types;
 
 import 'package:compiler/src/commandline_options.dart';
 import 'package:compiler/src/compiler.dart';
 import 'package:compiler/src/common_elements.dart';
 import 'package:compiler/src/elements/resolution_types.dart';
@@ skipping 405 matching lines @@
       NodeList arguments,
       CallStructure callStructure,
       _) {
     apply(arguments);
     return findReturnType(function.type);
   }
 }
 
 /// Computes the [ClassElement] implied by a type.
 // TODO(johnniwinther): Handle type variables, function types and typedefs.
-class ClassFinder extends BaseDartTypeVisitor<ClassElement, dynamic> {
+class ClassFinder extends BaseResolutionDartTypeVisitor<ClassElement, dynamic> {
   const ClassFinder();
 
   ClassElement findClass(ResolutionDartType type) => type.accept(this, null);
 
   @override
   ClassElement visitType(ResolutionDartType type, _) => null;
 
   @override
   ClassElement visitInterfaceType(ResolutionInterfaceType type, _) {
     return type.element;
   }
 }