[Sheriff] Mark flaky test on windows.

It was marked as flaky on linux nosnap, arm and nacl before. Now it's marked universally flaky since windows joined the list.

BUG=v8:2921
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/54713002

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@17506 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

test/mjsunit/mjsunit.status

@@ -35,10 +35,8 @@
 
   ##############################################################################
   # Flaky tests.
-  # BUG(v8:2921): Flaky on ia32 nosnap, arm and nacl.
-  'debug-step-4-in-frame': [PASS, [('system == linux and arch == ia32 or '
-                                    'arch == arm or arch == nacl_ia32 or '
-                                    'arch == nacl_x64'), FLAKY]],
+  # BUG(v8:2921).
+  'debug-step-4-in-frame': [PASS, FLAKY],
 
   ##############################################################################
   # Fails.