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

chrome/browser/extensions/extension_messages_apitest.cc

Index: chrome/browser/extensions/extension_messages_apitest.cc
diff --git a/chrome/browser/extensions/extension_messages_apitest.cc b/chrome/browser/extensions/extension_messages_apitest.cc
index a46af8931d25ba75877d99eee0d58725c5c4eebd..9bee026d46a10953412df31f28efbc67b37d83eb 100644
--- a/chrome/browser/extensions/extension_messages_apitest.cc
+++ b/chrome/browser/extensions/extension_messages_apitest.cc
@@ -121,8 +121,9 @@ class MessageSender : public content::NotificationObserver {
 };
 
 // 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