Disable flaky LockManagedGuestSessionNotManagedGuestSession test

TBR=jityao@google.com

Bug: 1075511
Change-Id: I6882a9f268492919903bceacd5bcdf78a2bb08e4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2167853Reviewed-by: Alexander Hendrich <hendrich@chromium.org>
Commit-Queue: Alexander Hendrich <hendrich@chromium.org>
Cr-Commit-Position: refs/heads/master@{#762799}

chrome/browser/chromeos/extensions/login_screen/login/login_apitest.cc

@@ -440,8 +440,9 @@ IN_PROC_BROWSER_TEST_F(LoginApitestWithEnterpriseUser,
       kUnlockManagedGuestSessionNotManagedGuestSession);
 }
 
+// TODO(https://crbug.com/1075511) Flaky test
 IN_PROC_BROWSER_TEST_F(LoginApitestWithEnterpriseUser,
-                       LockManagedGuestSessionNotManagedGuestSession) {
+                       DISABLED_LockManagedGuestSessionNotManagedGuestSession) {
   LoginUser();
   SetUpTestListeners();
   SetUpInSessionExtension();