Mark vm_timeline_flags_test as flaky everywhere.

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 4f929c10f16f3d5d2e7e146ea4ba867dc1148750..7e9b0d85feb9f3671b1845413a12fa97e053772b 100644
--- a/runtime/observatory/tests/service/service.status
+++ b/runtime/observatory/tests/service/service.status
@@ -9,6 +9,7 @@ reload_sources_test: Pass, Slow # Reload is slow on the bots
 get_retained_size_rpc_test: Pass, RuntimeError # Issue 28193
 pause_on_start_and_exit_test: Pass, RuntimeError # Issue 28624
 pause_on_start_then_step_test: Pass, RuntimeError # Issue 28624
+vm_timeline_flags_test: Pass, RuntimeError # Issue 28625
 
 [ ($compiler == none || $compiler == precompiler) && ($runtime == vm || $runtime == dart_precompiled) ]
 evaluate_activation_test/instance: RuntimeError # http://dartbug.com/20047
@@ -80,9 +81,6 @@ dev_fs_weird_char_test: Skip # Windows disallows question mark in paths
 dev_fs_http_put_weird_char_test: Skip # Windows disallows carriage returns in paths
 complex_reload_test: Skip # Issue 27861
 
-# Flaky test, only observed on Windows so far.
-vm_timeline_flags_test: Pass, RuntimeError # Issue 28625
-
 # Service protocol is not supported in product mode.
 [ $mode == product ]
 *: SkipByDesign