Remove AsyncError with Expando.

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:isolate';
 import 'dart:uri';
@@ skipping 124 matching lines @@
         if (request.uri.path == "/echo") {
           _handleEchoRequest(request, request.response);
         } else if (request.uri.path == '/ws') {
           _handleWebSocketRequest(request);
         } else {
           _handleFileOrDirectoryRequest(
               request, request.response, allowedPort);
         }
       },
       onError: (e) {
-        DebugLogger.error('HttpServer: an error occured: $e');
+        DebugLogger.error('HttpServer: an error occured', e);
       });
       _serverList.add(httpServer);
     });
   }
 
   void _handleFileOrDirectoryRequest(HttpRequest request,
                                      HttpResponse response,
                                      int allowedPort) {
     var path = _getFilePathFromRequestPath(request.uri.path);
     if (path != null) {
@@ skipping 23 matching lines @@
       } else {
         _sendNotFound(request, response);
       }
     }
   }
 
   void _handleEchoRequest(HttpRequest request, HttpResponse response) {
     response.headers.set("Access-Control-Allow-Origin", "*");
     request.pipe(response).catchError((e) {
       DebugLogger.warning(
-          'HttpServer: error while closing the response stream: $e');
+          'HttpServer: error while closing the response stream', e);
     });
   }
 
   void _handleWebSocketRequest(HttpRequest request) {
     WebSocketTransformer.upgrade(request).then((websocket) {
       websocket.listen((data) {
         websocket.send(data);
         websocket.close();
       }, onError: (e) {
-        DebugLogger.warning(
-            'HttpServer: error while echoing to WebSocket: $e');
+        DebugLogger.warning('HttpServer: error while echoing to WebSocket', e);
       });
     }).catchError((e) {
       DebugLogger.warning(
-          'HttpServer: error while transforming to WebSocket: $e');
+          'HttpServer: error while transforming to WebSocket', e);
     });
   }
 
   Path _getFilePathFromRequestPath(String urlRequestPath) {
     // Go to the top of the file to see an explanation of the URL path scheme.
     var requestPath = new Path(urlRequestPath.substring(1)).canonicalize();
     var pathSegments = requestPath.segments();
     if (pathSegments.length > 0) {
       var basePath;
       var relativePath;
@@ skipping 64 matching lines @@
     response.write(header);
     for (var entry in entries) {
       response.write(
           '<li><a href="${new Path(request.uri.path).append(entry.name)}">'
           '${entry.displayName}</a></li>');
     }
     response.write(footer);
     response.close();
     response.done.catchError((e) {
       DebugLogger.warning(
-          'HttpServer: error while closing the response stream: $e');
+          'HttpServer: error while closing the response stream', e);
     });
   }
 
   void _sendFileContent(HttpRequest request,
                         HttpResponse response,
                         int allowedPort,
                         Path path,
                         File file) {
     if (allowedPort != -1) {
       var headerOrigin = request.headers.value('Origin');
@@ skipping 29 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');
     }
     file.openRead().pipe(response).catchError((e) {
       DebugLogger.warning(
-          'HttpServer: error while closing the response stream: $e');
+          'HttpServer: error while closing the response stream', e);
     });
   }
 
   void _sendNotFound(HttpRequest request, HttpResponse response) {
     // NOTE: Since some tests deliberately try to access non-existent files.
     // We might want to remove this warning (otherwise it will show
     // up in the debug.log every time).
     if (request.uri.path != "/favicon.ico") {
       DebugLogger.warning('HttpServer: could not find file for request path: '
                           '"${request.uri.path}"');
     }
     response.statusCode = HttpStatus.NOT_FOUND;
     response.close();
     response.done.catchError((e) {
       DebugLogger.warning(
-          'HttpServer: error while closing the response stream: $e');
+          'HttpServer: error while closing the response stream', e);
     });
   }
 }
 
 // Helper class for displaying directory listings.
 class _Entry {
   final String name;
   final String displayName;
 
   _Entry(this.name, this.displayName);
 
   int compareTo(_Entry other) {
     return name.compareTo(other.name);
   }
 }