Go into UPGRADED state in http-parser, when socket is being detached.

sdk/lib/io/http_parser.dart

Index: sdk/lib/io/http_parser.dart
diff --git a/sdk/lib/io/http_parser.dart b/sdk/lib/io/http_parser.dart
index dee7371687749e0f3e0ae4bb8b65e22eaf254879..5c3263f00217e57f932ca579d7d6c9fa9f50f764 100644
--- a/sdk/lib/io/http_parser.dart
+++ b/sdk/lib/io/http_parser.dart
@@ -884,6 +884,8 @@ class _HttpParser
   void set responseToMethod(String method) { _responseToMethod = method; }
 
   _HttpDetachedIncoming detachIncoming() {
+    // Simulate detached by marking as upgraded.
+    _state = _State.UPGRADED;
     return new _HttpDetachedIncoming(_socketSubscription,
                                      readUnparsedData());
   }