[Sheriff] Disable ExtensionContextMenuLazyTest.IncognitoSplit on Windows/Mac for real

crrev.com/726101 intended to do this it seems but only covered
IncognitoSplitContextMenuCount.

IncognitoSplit is still flakily timing out on multiple Windows/Mac bots:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=EventPage/ExtensionContextMenuLazyTest.IncognitoSplit/0

Most often on win-asan and dbg bots,
e.g. https://ci.chromium.org/p/chromium/builders/ci/win-asan/9190
suggesting a race (those bots are slower and races resolve differently
on average) which results in a hang (hint:  awaited notification
arriving before the observer is installed is a typical reason for this).

The hang is @
ExtensionTestMessageListener::WaitUntilSatisfied @ extension_test_message_listener.cc:48
when invoked from
ASSERT_TRUE(onclick.WaitUntilSatisfied()) @ extension_context_menu_browsertest.cc:789

TBR=rdvelin.cronin@chromium.org

Bug: 1035062
Change-Id: I29f237b3acd311967d14cdc58d3489ddd5bfd767
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1980350
Commit-Queue: Gabriel Charette <gab@chromium.org>
Reviewed-by: Gabriel Charette <gab@chromium.org>
Cr-Commit-Position: refs/heads/master@{#727159}

chrome/browser/extensions/extension_context_menu_browsertest.cc

@@ -739,14 +739,14 @@ IN_PROC_BROWSER_TEST_P(ExtensionContextMenuLazyTest, TargetURLs) {
                                     std::string("item1")));
 }
 
-// Tests adding of context menus in incognito mode.
-#if defined(OS_LINUX)
-// Flakily hangs on Linux/CrOS - http://crbug.com/88317
+#if defined(OS_LINUX) || defined(OS_WIN) || defined(OS_MACOSX)
+// Flakily hangs on Linux/CrOS/Windows/Mac - http://crbug.com/1035062
 #define MAYBE_IncognitoSplit DISABLED_IncognitoSplit
 #else
 #define MAYBE_IncognitoSplit IncognitoSplit
 #endif
 
+// Tests adding of context menus in incognito mode.
 IN_PROC_BROWSER_TEST_P(ExtensionContextMenuLazyTest, MAYBE_IncognitoSplit) {
   ExtensionTestMessageListener created("created item regular", false);
   ExtensionTestMessageListener created_incognito("created item incognito",