Don't use linked maps/sets in http internals.

sdk/lib/io/http_impl.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.
 
 part of dart.io;
 
 const int _HEADERS_BUFFER_SIZE = 8 * 1024;
 
 class _HttpIncoming extends Stream<List<int>> {
   final int _transferLength;
@@ skipping 1470 matching lines @@
   final _HttpClientConnection connection;
   final _Proxy proxy;
 }
 
 
 class _HttpClient implements HttpClient {
   // TODO(ajohnsen): Use eviction timeout.
   bool _closing = false;
 
   final Map<String, Set<_HttpClientConnection>> _idleConnections
-      = new Map<String, Set<_HttpClientConnection>>();
+      = new HashMap<String, Set<_HttpClientConnection>>();
   final Set<_HttpClientConnection> _activeConnections
-      = new Set<_HttpClientConnection>();
+      = new HashSet<_HttpClientConnection>();
   final List<_Credentials> _credentials = [];
   final List<_ProxyCredentials> _proxyCredentials = [];
   Function _authenticate;
   Function _authenticateProxy;
   Function _findProxy = HttpClient.findProxyFromEnvironment;
   Duration _idleTimeout = const Duration(seconds: 15);
   Function _badCertificateCallback;
 
   Timer _noActiveTimer;
 
@@ skipping 170 matching lines @@
   }
 
   // Return a live connection to the idle pool.
   void _returnConnection(_HttpClientConnection connection) {
     _activeConnections.remove(connection);
     if (_closing) {
       connection.close();
       return;
     }
     if (!_idleConnections.containsKey(connection.key)) {
-      _idleConnections[connection.key] = new LinkedHashSet();
+      _idleConnections[connection.key] = new HashSet();
     }
     _idleConnections[connection.key].add(connection);
     connection.startTimer();
     _updateTimers();
   }
 
   // Remove a closed connnection from the active set.
   void _connectionClosed(_HttpClientConnection connection) {
     connection.stopTimer();
     _activeConnections.remove(connection);
@@ skipping 857 matching lines @@
 
 String _getHttpVersion() {
   var version = Platform.version;
   // Only include major and minor version numbers.
   int index = version.indexOf('.', version.indexOf('.') + 1);
   version = version.substring(0, index);
   return 'Dart/$version (dart:io)';
 }