Disable InstantExtendedTest.SearchDoesntReuseInstantTab on Mac too.

chrome/browser/ui/search/instant_extended_interactive_uitest.cc

 // Copyright 2013 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 <stdint.h>
 
 #include <sstream>
 
 #include "base/base_switches.h"
 #include "base/command_line.h"
@@ skipping 289 matching lines @@
         ThemeServiceFactory::GetThemeForProfile(
             ExtensionBrowserTest::browser()->profile());
     ASSERT_NE(static_cast<extensions::Extension*>(NULL), new_theme);
     ASSERT_EQ(new_theme->name(), theme_name);
   }
 
  private:
   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();
 
   SetOmniboxText("flowers");
   PressEnterAndWaitForFrameLoad();
 
   // Just did a regular search.
   content::WebContents* active_tab =
       browser()->tab_strip_model()->GetActiveWebContents();
   ASSERT_THAT(active_tab->GetURL().spec(), HasSubstr("q=flowers"));
@@ skipping 406 matching lines @@
   stream << "link.href = \"" << result_url.spec() << "\";";
   stream << "document.body.appendChild(link);";
   stream << "link.click();";
   EXPECT_TRUE(content::ExecuteScript(contents, stream.str()));
 
   content::WaitForLoadStop(contents);
   std::string expected_title =
       "Referrer is " + instant_url().GetWithEmptyPath().spec();
   EXPECT_EQ(ASCIIToUTF16(expected_title), contents->GetTitle());
 }