Add test directive to include other files used by a test in its compiled output directory.

tests/standalone/io/http_proxy_advanced_test.dart

Index: tests/standalone/io/http_proxy_advanced_test.dart
diff --git a/tests/standalone/io/http_proxy_advanced_test.dart b/tests/standalone/io/http_proxy_advanced_test.dart
index 7a349d18d4a0fc4e20719c19fd2ca56be2523b3f..8309fc7118f29dc8536deb86ff302903201e6390 100644
--- a/tests/standalone/io/http_proxy_advanced_test.dart
+++ b/tests/standalone/io/http_proxy_advanced_test.dart
@@ -2,6 +2,10 @@
 // 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.
 
+// OtherResources=certificates/server_chain.pem
+// OtherResources=certificates/server_key.pem
+// OtherResources=certificates/trusted_certs.pem
+
 import "package:convert/convert.dart";
 import "package:crypto/crypto.dart";
 import "package:expect/expect.dart";