[sheriff] Disable AutomationApiTest.TextareaAppendPerf on ChromeOS

TBR=abigailbklein@google.com
Bug: 1162238

Change-Id: I3223a7d38889f7a1925a37be5ede03839675cee6
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2633188Reviewed-by: Yi Gu <yigu@chromium.org>
Reviewed-by: Abigail Klein <abigailbklein@google.com>
Commit-Queue: Fabrice de Gans-Riberi <fdegans@chromium.org>
Commit-Queue: Yi Gu <yigu@chromium.org>
Auto-Submit: Fabrice de Gans-Riberi <fdegans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#844293}

chrome/browser/extensions/api/automation/automation_apitest.cc

@@ -475,7 +475,7 @@ IN_PROC_BROWSER_TEST_F(AutomationApiTest, AccessibilityFocus) {
       << message_;
 }
 
-#if BUILDFLAG(IS_CHROMEOS_ASH) && defined(MEMORY_SANITIZER)
+#if defined(OS_CHROMEOS)
 // TODO(http://crbug.com/1162238): flaky on ChromeOS.
 #define MAYBE_TextareaAppendPerf DISABLED_TextareaAppendPerf
 #else