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

sdk/lib/io/http_impl.dart

Index: sdk/lib/io/http_impl.dart
diff --git a/sdk/lib/io/http_impl.dart b/sdk/lib/io/http_impl.dart
index 7f7a73825dc91337f65b66bcd3a054584e2d1ba0..80c560ad69e7dc657a07a8d438d27380488880de 100644
--- a/sdk/lib/io/http_impl.dart
+++ b/sdk/lib/io/http_impl.dart
@@ -1488,9 +1488,9 @@ class _HttpClient implements HttpClient {
   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;
@@ -1681,7 +1681,7 @@ class _HttpClient implements HttpClient {
       return;
     }
     if (!_idleConnections.containsKey(connection.key)) {
-      _idleConnections[connection.key] = new LinkedHashSet();
+      _idleConnections[connection.key] = new HashSet();
     }
     _idleConnections[connection.key].add(connection);
     connection.startTimer();