HttpServer start async fix (#25394).

pkg/analysis_server/lib/src/server/http_server.dart

 // 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.
 
 library analysis_server.src.server.http_server;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:analysis_server/src/channel/web_socket_channel.dart';
@@ skipping 51 matching lines @@
     if (_printBuffer.length > MAX_PRINT_BUFFER_LENGTH) {
       _printBuffer.removeRange(
           0, _printBuffer.length - MAX_PRINT_BUFFER_LENGTH);
     }
   }
 
   /**
    * Begin serving HTTP requests over the given port.
    */
   void serveHttp(int port) {
-    try {
-      _server = HttpServer.bind(InternetAddress.LOOPBACK_IP_V4, port);
-      _server.then(_handleServer);
-    } catch (exception) {
-      // We were unable to start the server, and there's nothing we can do about
-      // it.
-    }
+    _server = HttpServer.bind(InternetAddress.LOOPBACK_IP_V4, port);
+    _server.then(_handleServer).catchError((_) {/* Ignore errors. */});
   }
 
   /**
    * Handle a GET request received by the HTTP server.
    */
   void _handleGetRequest(HttpRequest request) {
     if (getHandler == null) {
       getHandler = new GetHandler(socketServer, _printBuffer);
     }
     getHandler.handleGetRequest(request);
   }
 
   /**
    * Attach a listener to a newly created HTTP server.
    */
-  void _handleServer(HttpServer httServer) {
-    httServer.listen((HttpRequest request) {
+  void _handleServer(HttpServer httpServer) {
+    httpServer.listen((HttpRequest request) {
       List<String> updateValues = request.headers[HttpHeaders.UPGRADE];
       if (updateValues != null && updateValues.indexOf('websocket') >= 0) {
         WebSocketTransformer.upgrade(request).then((WebSocket websocket) {
           _handleWebSocket(websocket);
         });
       } else if (request.method == 'GET') {
         _handleGetRequest(request);
       } else {
         _returnUnknownRequest(request);
       }
@@ skipping 15 matching lines @@
    */
   void _returnUnknownRequest(HttpRequest request) {
     HttpResponse response = request.response;
     response.statusCode = HttpStatus.NOT_FOUND;
     response.headers.contentType =
         new ContentType("text", "plain", charset: "utf-8");
     response.write('Not found');
     response.close();
   }
 }