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 "

[vasilii, 2015/04/15 15:51:55]

I'd reverse the condition as "There is a corresponding credential with non-empty
username". Thus, it's definitely a bug in the password manager. While a
standalone empty username can mean anything.

[msramek, 2015/04/16 14:34:26]

Well, that was my original intention. But then I realized that the histograms
CountInDatabase and "PairedWithNonempty" will not be well readable together.
Sure, if "PairedWithNonempty" has almost the same distribution as
CountInDatabase, we know that this is the overwhelming cause. But if it's, for
example,

CountInDatabase PairedWithNonempty
2: 1 user       1: 1 user  
3: 1 user       2: 1 user  

we won't be able to tell if only one or both of the people encountered an empty
password form.

I think this solution gives us a more interesting information, "How many empty
usernames (per user) are there, that we do not know the cause for yet?"

and the goal of this investigation is to define a histogram that has flat
zeroes.

+                     "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."
+                             "NotPairedWithNonempty",

[Ilya Sherman, 2015/04/15 22:56:05]

nit: Rather than splitting this string across multiple lines, please just wrap
the arguments, i.e.

    UMA_HISTOGRAM_COUNTS_100(
      "PasswordManager.EmptyUsernames.NotPairedWithNonempty", num_entries);

[msramek, 2015/04/16 14:34:26]

Done.

+                             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