[Switch Access] Prevent repeated crash after enable on login screen

A bug was recently found where enabling Switch Access on the login
screen leads to a series of crashes. This is a short-term fix which
prevents the crash by removing the option to enable Switch Access when
the login state is NOT_LOGGED_IN.

R=katie@chromium.org
TBR=skuhne@chromium.org

AX-Relnotes: n/a.
Bug: 1108808
Change-Id: Ie718cda7aaa8c544b0a0cc49615cd1b802f1d353
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2316437
Commit-Queue: Anastasia Helfinstein <anastasi@google.com>
Reviewed-by: Katie Dektar <katie@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791355}

ash/accessibility/accessibility_controller_impl.cc

@@ -20,6 +20,7 @@
 #include "ash/high_contrast/high_contrast_controller.h"
 #include "ash/keyboard/keyboard_controller_impl.h"
 #include "ash/keyboard/ui/keyboard_util.h"
+#include "ash/login_status.h"
 #include "ash/policy/policy_recommendation_restorer.h"
 #include "ash/public/cpp/accessibility_controller_client.h"
 #include "ash/public/cpp/ash_constants.h"
@@ -1121,6 +1122,13 @@ bool AccessibilityControllerImpl::IsSwitchAccessRunning() const {
 }
 
 bool AccessibilityControllerImpl::IsSwitchAccessSettingVisibleInTray() {
+  // Switch Access cannot be enabled on the sign-in page until crbug/1108808 has
+  // been fully resolved.
+  if (!switch_access().enabled() &&
+      Shell::Get()->session_controller()->login_status() ==
+          ash::LoginStatus::NOT_LOGGED_IN) {
+    return false;
+  }
   return switch_access().IsVisibleInTray();
   return IsEnterpriseIconVisibleInTrayMenu(
       prefs::kAccessibilitySwitchAccessEnabled);