Disable flaky GaiaAuthOffline test

LoginTest.GaiaAuthOffline is failing often on the
linux-chromeos-google-rel bot. Example failure:
https://ci.chromium.org/p/chrome/builders/ci/linux-chromeos-google-rel/9135

Disabling the test for now

TBR=antrim@chromium.org

Bug: 1023591
Change-Id: I1aced34639a552c0badea33f3787358d898c5b9a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1917879Reviewed-by: Tommy Steimel <steimel@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#715415}

chrome/browser/chromeos/login/login_browsertest.cc

@@ -153,7 +153,8 @@ IN_PROC_BROWSER_TEST_F(LoginTest, PRE_GaiaAuthOffline) {
   offline_gaia_test_mixin_.PrepareOfflineGaiaLogin();
 }
 
-IN_PROC_BROWSER_TEST_F(LoginTest, GaiaAuthOffline) {
+// Flaking: https://crbug.com/1023591
+IN_PROC_BROWSER_TEST_F(LoginTest, DISABLED_GaiaAuthOffline) {
   offline_gaia_test_mixin_.GoOffline();
   offline_gaia_test_mixin_.SignIn(test_user_.account_id, kPassword);
   TestSystemTrayIsVisible(false);