Add exception information to help diagnose issue 8865

tests/standalone/io/http_content_length_test.dart

Index: tests/standalone/io/http_content_length_test.dart
diff --git a/tests/standalone/io/http_content_length_test.dart b/tests/standalone/io/http_content_length_test.dart
index 14d4000fd170a61e24464303ab8826f85f1ac3e9..61156827e3a4962b6fc1bbda55a31b49248851d2 100644
--- a/tests/standalone/io/http_content_length_test.dart
+++ b/tests/standalone/io/http_content_length_test.dart
@@ -1,4 +1,4 @@
-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
@@ -91,7 +91,7 @@ void testBody(int totalConnections, bool useHeader) {
                       Expect.fail("Unexpected successful response completion");
                     })
                     .catchError((e) {
-                      Expect.isTrue(e.error is HttpException);
+                      Expect.isTrue(e.error is HttpException, "[$e] [${e.error}]");
                     });
                 response.close();
                 Expect.throws(() => response.addString("x"),