Unify the server and plugin versions of the generators

pkg/analyzer_plugin/tool/spec/codegen_dart.dart

-// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2014, 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.
 
 import 'api.dart';
 
 /**
  * Visitor specialized for generating Dart code.
  */
 class DartCodegenVisitor extends HierarchicalApiVisitor {
   /**
@@ skipping 28 matching lines @@
       return 'List<${dartType(type.itemType)}>';
     } else if (type is TypeMap) {
       return 'Map<${dartType(type.keyType)}, ${dartType(type.valueType)}>';
     } else if (type is TypeUnion) {
       return 'dynamic';
     } else {
       throw new Exception("Can't convert to a dart type");
     }
   }
 }