Mark another test as flaky on mac to try and keep the bot greener...

chrome/test/startup/shutdown_test.cc

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/environment.h"
 #include "base/file_util.h"
 #include "base/path_service.h"
 #include "base/platform_thread.h"
 #include "base/string_number_conversions.h"
 #include "base/string_util.h"
@@ skipping 108 matching lines @@
 }
 
 TEST_F(ShutdownTest, SimpleUserQuit) {
   RunShutdownTest("shutdown", "simple-user-quit",
                   true, /* important */ SIMPLE, UITest::USER_QUIT);
 }
 
 // http://crbug.com/52858
 #if defined(OS_MACOSX)
 #define MAYBE_SimpleSessionEnding FLAKY_SimpleSessionEnding
+#define MAYBE_TwentyTabsWindowClose FLAKY_TwentyTabsWindowClose
 #define MAYBE_TwentyTabsUserQuit FLAKY_TwentyTabsUserQuit
 #else
 #define MAYBE_SimpleSessionEnding SimpleSessionEnding
+#define MAYBE_TwentyTabsWindowClose TwentyTabsWindowClose
 #define MAYBE_TwentyTabsUserQuit TwentyTabsUserQuit
 #endif
 
 TEST_F(ShutdownTest, MAYBE_SimpleSessionEnding) {
   RunShutdownTest("shutdown", "simple-session-ending",
                   true, /* important */ SIMPLE, UITest::SESSION_ENDING);
 }
 
-TEST_F(ShutdownTest, TwentyTabsWindowClose) {
+TEST_F(ShutdownTest, MAYBE_TwentyTabsWindowClose) {
   RunShutdownTest("shutdown", "twentytabs-window-close",
                   true, /* important */ TWENTY_TABS, UITest::WINDOW_CLOSE);
 }
 
 TEST_F(ShutdownTest, MAYBE_TwentyTabsUserQuit) {
   RunShutdownTest("shutdown", "twentytabs-user-quit",
                   true, /* important */ TWENTY_TABS, UITest::USER_QUIT);
 }
 
 // http://crbug.com/40671
 #if defined(OS_WIN) && !defined(NDEBUG)
 #define MAYBE_TwentyTabsSessionEnding DISABLED_TwentyTabsSessionEnding
 #else
 #define MAYBE_TwentyTabsSessionEnding TwentyTabsSessionEnding
 #endif
 
 TEST_F(ShutdownTest, MAYBE_TwentyTabsSessionEnding) {
   RunShutdownTest("shutdown", "twentytabs-session-ending",
                   true, /* important */ TWENTY_TABS, UITest::SESSION_ENDING);
 }
 
 }  // namespace