Refactor DartTypeVisitor and ElementVisitor.

pkg/compiler/lib/src/js_backend/namer.dart

 // Copyright (c) 2011, 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.
 
 part of js_backend;
 
 /**
  * Assigns JavaScript identifiers to Dart variables, class-names and members.
  *
  * Names are generated through three stages:
@@ skipping 1693 matching lines @@
     return hash;
   }
 
   static int _finish(int hash) {
     hash = _MASK & (hash + (((_MASK >> 3) & hash) <<  3));
     hash = hash & (hash >> 11);
     return _MASK & (hash + (((_MASK >> 15) & hash) << 15));
   }
 }
 
-class FunctionTypeNamer extends DartTypeVisitor {
+class FunctionTypeNamer extends BaseDartTypeVisitor {
   final Compiler compiler;
   StringBuffer sb;
 
   FunctionTypeNamer(this.compiler);
 
   JavaScriptBackend get backend => compiler.backend;
 
   String computeName(DartType type) {
     sb = new StringBuffer();
     visit(type);
     return sb.toString();
   }
 
-  visit(DartType type) {
+  visit(DartType type, [_]) {
     type.accept(this, null);
   }
 
   visitType(DartType type, _) {
     sb.write(type.name);
   }
 
   visitFunctionType(FunctionType type, _) {
     if (backend.rti.isSimpleFunctionType(type)) {
       sb.write('args${type.parameterTypes.length}');
@@ skipping 20 matching lines @@
         if (!first) {
           sb.write('_');
         }
         sb.write('_');
         visit(parameter);
         first = true;
       }
     }
   }
 }