Report the number of empty usernames without a nonempty pair.

components/password_manager/core/browser/login_database.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/password_manager/core/browser/login_database.h"
 
 #include <algorithm>
 #include <limits>
 
 #include "base/bind.h"
@@ skipping 486 matching lines @@
                             4);
 
   sql::Statement empty_usernames_statement(db_.GetCachedStatement(
       SQL_FROM_HERE, "SELECT COUNT(*) FROM logins "
                      "WHERE blacklisted_by_user=0 AND username_value=''"));
   if (empty_usernames_statement.Step()) {
     int empty_forms = empty_usernames_statement.ColumnInt(0);
     UMA_HISTOGRAM_COUNTS_100("PasswordManager.EmptyUsernames.CountInDatabase",
                              empty_forms);
   }
+
+  sql::Statement standalone_empty_usernames_statement(db_.GetCachedStatement(
+      SQL_FROM_HERE, "SELECT COUNT(*) FROM logins a "
+                     "WHERE a.blacklisted_by_user=0 AND a.username_value='' "
+                     "AND NOT EXISTS (SELECT * FROM logins b "
+                     "WHERE b.blacklisted_by_user=0 AND b.username_value!='' "
+                     "AND a.signon_realm = b.signon_realm)"));
+  if (standalone_empty_usernames_statement.Step()) {
+    int num_entries = standalone_empty_usernames_statement.ColumnInt(0);
+    UMA_HISTOGRAM_COUNTS_100(
+        "PasswordManager.EmptyUsernames.WithoutCorrespondingNonempty",
+        num_entries);
+  }
 }
 
 PasswordStoreChangeList LoginDatabase::AddLogin(const PasswordForm& form) {
   PasswordStoreChangeList list;
   if (!DoesMatchConstraints(form))
     return list;
   std::string encrypted_password;
   if (EncryptedString(form.password_value, &encrypted_password) !=
       ENCRYPTION_RESULT_SUCCESS)
     return list;
@@ skipping 415 matching lines @@
     UMA_HISTOGRAM_ENUMERATION("PasswordManager.PslDomainMatchTriggering",
                               psl_domain_match_metric, PSL_DOMAIN_MATCH_COUNT);
   }
 
   if (!statement->Succeeded())
     return false;
   return true;
 }
 
 }  // namespace password_manager