Add test/xml content type to test server.

tools/testing/dart/http_server.dart

 // Copyright (c) 2013, 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 http_server;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'dart:convert' show
@@ skipping 383 matching lines @@
       }
     }
     if (path.filename.endsWith('.html')) {
       response.headers.set('Content-Type', 'text/html');
     } else if (path.filename.endsWith('.js')) {
       response.headers.set('Content-Type', 'application/javascript');
     } else if (path.filename.endsWith('.dart')) {
       response.headers.set('Content-Type', 'application/dart');
     } else if (path.filename.endsWith('.css')) {
       response.headers.set('Content-Type', 'text/css');
+    } else if (path.filename.endsWith('.xml')) {
+      response.headers.set('Content-Type', 'text/xml');
     }
     response.headers.removeAll("X-Frame-Options");
     file.openRead().pipe(response).catchError((e) {
       DebugLogger.warning(
           'HttpServer: error while closing the response stream', e);
     });
   }
 
   void _sendNotFound(HttpRequest request) {
     bool isHarmlessPath(String path) {
@@ skipping 39 matching lines @@
 class _Entry implements Comparable {
   final String name;
   final String displayName;
 
   _Entry(this.name, this.displayName);
 
   int compareTo(_Entry other) {
     return name.compareTo(other.name);
   }
 }