Disable flaky ChromeVoxEventWatcherUnitTest.AriaHiddenFeedback

Bug: 622387, 919033
Tbr: dtseng
Change-Id: I03834f051d3368d2a6f497e918d20bb3e630301e
Reviewed-on: https://chromium-review.googlesource.com/c/1396141Reviewed-by: Max Morin <maxmorin@chromium.org>
Commit-Queue: Max Morin <maxmorin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619919}

chrome/browser/resources/chromeos/chromevox/chromevox/injected/event_watcher_test.unitjs

@@ -503,7 +503,8 @@ SYNC_TEST_F('ChromeVoxEventWatcherUnitTest', 'ShouldWaitToProcess', function() {
  * Test that no feedback is received for events that fire on elements
  * that are hidden (or the descendant of a hidden element).
  */
-TEST_F('ChromeVoxEventWatcherUnitTest', 'AriaHiddenFeedback', function() {
+// Flaky on Chromium OS: https://crbug.com/919033.
+TEST_F('ChromeVoxEventWatcherUnitTest', 'DISABLED_AriaHiddenFeedback', function() {
   this.loadHtml('<div>' +
       '<div>' +
       '  <button id="button1">Button 1</button>' +