Add UMA histograms for tracking empty usernames.

components/password_manager/core/browser/login_database_unittest.cc

Index: components/password_manager/core/browser/login_database_unittest.cc
diff --git a/components/password_manager/core/browser/login_database_unittest.cc b/components/password_manager/core/browser/login_database_unittest.cc
index b5562617a30f02f010fd96d7180c176502df99c4..97c566ce08fd34cb0042574272acc7443a31c5d7 100644
--- a/components/password_manager/core/browser/login_database_unittest.cc
+++ b/components/password_manager/core/browser/login_database_unittest.cc
@@ -1041,17 +1041,30 @@ TEST_F(LoginDatabaseTest, ReportMetricsTest) {
   password_form.times_used = 4;
   EXPECT_EQ(AddChangeForForm(password_form), db().AddLogin(password_form));
 
+  password_form.origin = GURL("http://fourth.example.com/");
+  password_form.signon_realm = "http://fourth.example.com/";
+  password_form.type = PasswordForm::TYPE_MANUAL;
+  password_form.username_value = ASCIIToUTF16("");
+  password_form.times_used = 10;
+  EXPECT_EQ(AddChangeForForm(password_form), db().AddLogin(password_form));
+
+  password_form.origin = GURL("http://fifth.example.com/");
+  password_form.signon_realm = "http://fifth.example.com/";
+  password_form.password_value = ASCIIToUTF16("");
+  password_form.blacklisted_by_user = true;
+  EXPECT_EQ(AddChangeForForm(password_form), db().AddLogin(password_form));
+
   base::HistogramTester histogram_tester;
   db().ReportMetrics("", false);
 
   histogram_tester.ExpectUniqueSample(
       "PasswordManager.TotalAccounts.UserCreated.WithoutCustomPassphrase",
-      3,
+      4,
       1);
   histogram_tester.ExpectBucketCount(
       "PasswordManager.AccountsPerSite.UserCreated.WithoutCustomPassphrase",
       1,
-      1);
+      2);
   histogram_tester.ExpectBucketCount(
       "PasswordManager.AccountsPerSite.UserCreated.WithoutCustomPassphrase",
       2,
@@ -1084,6 +1097,10 @@ TEST_F(LoginDatabaseTest, ReportMetricsTest) {
       "PasswordManager.TimesPasswordUsed.AutoGenerated.WithoutCustomPassphrase",
       4,
       1);
+  histogram_tester.ExpectUniqueSample(
+      "PasswordManager.EmptyUsernames.CountInDatabase",
+      1,
+      1);
 }
 
 #if defined(OS_POSIX)