Update status for flaky VM service tests.

runtime/observatory/tests/service/service.status

Index: runtime/observatory/tests/service/service.status
diff --git a/runtime/observatory/tests/service/service.status b/runtime/observatory/tests/service/service.status
index bb742acc232c0cccfc6083f24449bbc812960b06..726fb3ee595ec98ff680c4fca15f234ab20df5e9 100644
--- a/runtime/observatory/tests/service/service.status
+++ b/runtime/observatory/tests/service/service.status
@@ -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.
 
+# Flaky failures
+vm_timeline_flags_test: Pass, RuntimeError # Issue 26483
+gc_test: Pass, RuntimeError # Issue 26490
+
 [ ($compiler == none || $compiler == precompiler) && ($runtime == vm || $runtime == dart_precompiled) ]
 evaluate_activation_test/instance: RuntimeError # http://dartbug.com/20047
 evaluate_activation_test/scope: RuntimeError # http://dartbug.com/20047