Disable InstantExtendedTest.SearchDoesntReuseInstantTab on Mac too.

chrome/browser/ui/search/instant_extended_interactive_uitest.cc

Index: chrome/browser/ui/search/instant_extended_interactive_uitest.cc
diff --git a/chrome/browser/ui/search/instant_extended_interactive_uitest.cc b/chrome/browser/ui/search/instant_extended_interactive_uitest.cc
index 481e367b20957b8859dc6f4a47dfe06f5378370f..0dfe420b89a783f2486e1cb1c855718c279d67bd 100644
--- a/chrome/browser/ui/search/instant_extended_interactive_uitest.cc
+++ b/chrome/browser/ui/search/instant_extended_interactive_uitest.cc
@@ -307,13 +307,9 @@ class InstantPolicyTest : public ExtensionBrowserTest, public InstantTestBase {
   DISALLOW_COPY_AND_ASSIGN(InstantPolicyTest);
 };
 
-// Flaky on Windows in the CQ and Linux memory bot: https://crbug.com/678975
-#if defined(OS_WIN) || defined(OS_LINUX)
-#define MAYBE_SearchDoesntReuseInstantTab DISABLED_SearchDoesntReuseInstantTab
-#else
-#define MAYBE_SearchDoesntReuseInstantTab SearchDoesntReuseInstantTab
-#endif
-IN_PROC_BROWSER_TEST_F(InstantExtendedTest, MAYBE_SearchDoesntReuseInstantTab) {
+// TODO(https://crbug.com/678975): Flaky on memory bot (all platforms).
+IN_PROC_BROWSER_TEST_F(InstantExtendedTest,
+                       DISABLED_SearchDoesntReuseInstantTab) {
   ASSERT_NO_FATAL_FAILURE(SetupInstant(browser()));
   FocusOmnibox();