Disable flakey test.

chrome/browser/chromeos/login/existing_user_controller_browsertest.cc

Index: chrome/browser/chromeos/login/existing_user_controller_browsertest.cc
diff --git a/chrome/browser/chromeos/login/existing_user_controller_browsertest.cc b/chrome/browser/chromeos/login/existing_user_controller_browsertest.cc
index 50da26e57c7d704b7759d029db794943ee408354..3432f9d7ab7874343325e343b25d124920f17b42 100644
--- a/chrome/browser/chromeos/login/existing_user_controller_browsertest.cc
+++ b/chrome/browser/chromeos/login/existing_user_controller_browsertest.cc
@@ -543,8 +543,11 @@ IN_PROC_BROWSER_TEST_F(ExistingUserControllerPublicSessionTest,
   EXPECT_FALSE(auto_login_timer()->IsRunning());
 }
 
+// Disable since the flake from this test makes it hard to track down other
+// problems on the bots.
+// See https://crbug.com/644205 or https://crbug.com/516015 .
 IN_PROC_BROWSER_TEST_F(ExistingUserControllerPublicSessionTest,
-                       AutoLoginNoDelay) {
+                       DISABLED_AutoLoginNoDelay) {
   // Set up mocks to check login success.
   UserContext user_context(user_manager::USER_TYPE_PUBLIC_ACCOUNT,
                            public_session_account_id_);