Log when we advance from one authentication method to another

This will be helpful e.g. when trying to match logs with behavior as
reported e.g. in crbug.com/1002617 (where logs don't match with the
customer story but we can't be 100% sure).

We log usin LOG(WARNING) as we expect the first auth to work, so this
is an exceptional condition.

Bug: chromium:1002617
Test: N/A
Change-Id: I4366445f9691e527218b907c5ce1debd19f37aa5
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1827937
Commit-Queue: Pavol Marko <pmarko@chromium.org>
Reviewed-by: Pavol Marko <pmarko@chromium.org>
Auto-Submit: Yves Arrouye <drcrash@chromium.org>
Cr-Commit-Position: refs/heads/master@{#700370}

chrome/browser/chromeos/login/enrollment/enrollment_screen.cc

@@ -194,6 +194,8 @@ void EnrollmentScreen::SetConfig() {
 
 bool EnrollmentScreen::AdvanceToNextAuth() {
   if (current_auth_ != last_auth_ && current_auth_ == AUTH_ATTESTATION) {
+    LOG(WARNING) << "User stopped using auth: " << current_auth_
+                 << ", current auth: " << last_auth_ << ".";
     current_auth_ = last_auth_;
     SetConfig();
     return true;
@@ -315,7 +317,7 @@ void EnrollmentScreen::AutomaticRetry() {
 void EnrollmentScreen::ProcessRetry() {
   ++num_retries_;
   LOG(WARNING) << "Enrollment retries: " << num_retries_
-               << ", current_auth_: " << current_auth_;
+               << ", current auth: " << current_auth_ << ".";
   Show();
 }