Add a password field count histogram for empty usernames investigation.

components/autofill/content/renderer/password_form_conversion_utils.cc

 // Copyright 2013 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/autofill/content/renderer/password_form_conversion_utils.h"
 
 #include <vector>
 
 #include "base/lazy_instance.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 409 matching lines @@
     if (HasAutocompleteAttributeValue(new_password, "new-password"))
       password_form->new_password_marked_by_site = true;
   }
 
   if (username_element.isNull()) {
     // To get a better idea on how password forms without a username field
     // look like, report the total number of text and password fields.
     UMA_HISTOGRAM_COUNTS_100(
         "PasswordManager.EmptyUsernames.TextAndPasswordFieldCount",
         layout_sequence.size());
+    // For comparison, also report the number of password fields.
+    UMA_HISTOGRAM_COUNTS_100(
+        "PasswordManager.EmptyUsernames.PasswordFieldCount",
+        std::count(layout_sequence.begin(), layout_sequence.end(), 'P'));
   }
 
   password_form->scheme = PasswordForm::SCHEME_HTML;
   password_form->ssl_valid = false;
   password_form->preferred = false;
   password_form->blacklisted_by_user = false;
   password_form->type = PasswordForm::TYPE_MANUAL;
 }
 
 GURL StripAuthAndParams(const GURL& gurl) {
@@ skipping 42 matching lines @@
   WebFormElementToFormData(web_form,
                            blink::WebFormControlElement(),
                            EXTRACT_NONE,
                            &password_form->form_data,
                            NULL /* FormFieldData */);
 
   return password_form.Pass();
 }
 
 }  // namespace autofill