Fix multiple close of incoming in _HttpParser.

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 cd088e224780c9d71da522dcab5376b3f8cffdf6..908c990965f52e2212983b32014e542a86ca340e 100644
--- a/sdk/lib/io/http_parser.dart
+++ b/sdk/lib/io/http_parser.dart
@@ -882,7 +882,8 @@ class _HttpParser
   }
 
   void _closeIncoming() {
-    assert(_incoming != null);
+    // Ignore multiple close (can happend in re-entrance).
+    if (_incoming == null) return;
     var tmp = _incoming;
     _incoming = null;
     tmp.close();