Disable flaky AccessibilityEventsAriaComboBoxDelayAddList on Mac

See https://crbug.com/945193#c13

TBR=aboxhall@chromium.org

Bug: 945193
Change-Id: Ia0db3f40992a95707f38170fb5f9823305c73b3d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2472158Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: Michael Wasserman <msw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#817123}

content/browser/accessibility/dump_accessibility_events_browsertest.cc

@@ -393,8 +393,9 @@ IN_PROC_BROWSER_TEST_P(DumpAccessibilityEventsTest,
   RunEventTest(FILE_PATH_LITERAL("aria-combo-box-focus.html"));
 }
 
-// TODO(835455): Fails on Windows.
-#if defined(OS_WIN)
+// TODO(crbug.com/835455): Fails on Windows.
+// TODO(crbug.com/945193): Flaky on Mac.
+#if defined(OS_WIN) || defined(OS_MAC)
 #define MAYBE_AccessibilityEventsAriaComboBoxDelayAddList \
   DISABLED_AccessibilityEventsAriaComboBoxDelayAddList
 #else