[ChromeOS][Flaky] Disable three flaky ChromeVox tests

This CL disabled these flaky tests:
TextFocusFeedback
DoubleFocusAlertDialogFeedback
ToggleOnKeyUp

They have caused failures recently and show a history of flakiness:
https://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=ChromeVoxEventWatcherUnitTest

TBR=dmazzoni@chromium.org

Bug: 912390, 622387
Change-Id: If7647be13420ff98df3a51d0fa156635f181c074
Reviewed-on: https://chromium-review.googlesource.com/c/1371476
Reviewed-by: Friedrich Horschig [CET] <fhorschig@chromium.org>
Commit-Queue: Friedrich Horschig [CET] <fhorschig@chromium.org>
Cr-Commit-Position: refs/heads/master@{#615495}
1 file changed