Disable ExtensionApiTest.Messaging for OS_MACOSX as it is timeout/flaky

chrome/browser/extensions/extension_messages_apitest.cc

 // Copyright (c) 2012 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 <stddef.h>
 #include <stdint.h>
 
 #include <memory>
 #include <utility>
 
@@ skipping 103 matching lines @@
     event_router->BroadcastEvent(BuildEvent(
         BuildEventArguments(true, "last message"),
         content::Source<Profile>(source).ptr(),
         GURL()));
   }
 
   content::NotificationRegistrar registrar_;
 };
 
 // Tests that message passing between extensions and content scripts works.
-#if defined(MEMORY_SANITIZER)
-// https://crbug.com/582185
+#if defined(MEMORY_SANITIZER) || defined(OS_MACOSX)
+// https://crbug.com/582185 - flakily times out on Linux/CrOS MSAN
+// https://crbug.com/681705 - flakily times out on mac_chromium_rel_ng
 #define MAYBE_Messaging DISABLED_Messaging
 #else
 #define MAYBE_Messaging Messaging
 #endif
 IN_PROC_BROWSER_TEST_F(ExtensionApiTest, MAYBE_Messaging) {
   ASSERT_TRUE(StartEmbeddedTestServer());
   ASSERT_TRUE(RunExtensionTest("messaging/connect")) << message_;
 }
 
 IN_PROC_BROWSER_TEST_F(ExtensionApiTest, MessagingCrash) {
@@ skipping 1187 matching lines @@
   ASSERT_TRUE(content::ExecuteScriptAndExtractInt(
       background_contents,
       "window.domAutomationController.send(window.messageCount);",
       &message_count));
   EXPECT_EQ(1, message_count);
 }
 
 }  // namespace
 
 };  // namespace extensions