Something seems to time out and fail after about 20 seconds. It's not flaky on regular browser_tests.

https://test-results.appspot.com/dashboards/flakiness_dashboard.html#testType=mash_browser_tests&builder=chromium.fyi%3AMojo%20ChromiumOS

https://chromium-swarm.appspot.com/task?id=39bb52318781be10&refresh=10&show_raw=1

[9884:9884:1109/123835.304881:ERROR:remote_text_input_client.cc(135)] Not implemented reached in virtual void RemoteTextInputClient::OnInputMethodChanged()
[9884:9884:1109/123835.304911:ERROR:remote_text_input_client.cc(92)] Not implemented reached in virtual bool RemoteTextInputClient::HasCompositionText() const
[9884:9884:1109/123835.304921:ERROR:remote_text_input_client.cc(98)] Not implemented reached in virtual bool RemoteTextInputClient::GetTextRange(gfx::Range *) const
[9884:9884:1109/123835.304928:ERROR:remote_text_input_client.cc(153)] Not implemented reached in virtual void RemoteTextInputClient::EnsureCaretNotInRect(const gfx::Rect &)
[9884:9884:1109/123835.317019:ERROR:layer_tree_host_impl.cc(2505)] Forcing zero-copy tile initialization as worker context is missing
[1:1:1109/123835.325215:WARNING:app_launch_info.cc(280)] Override URL passed for Web Store should not contain a port.  Removing it.
[9884:9884:1109/123835.404751:ERROR:layer_tree_host_impl.cc(2505)] Forcing zero-copy tile initialization as worker context is missing
[1:10:1109/123835.435434:ERROR:layer_tree_host_impl.cc(2505)] Forcing zero-copy tile initialization as worker context is missing
[9884:9991:1109/123835.644843:WARNING:child_process_launcher_helper_posix.cc(118)] Ignoring invalid file v8_context_snapshot.bin
../../chrome/browser/chromeos/app_mode/kiosk_app_manager_browsertest.cc:598: Failure
Value of: put_waiter.success()
  Actual: false
Expected: true