Add UMA histograms for tracking empty usernames.

chrome/browser/ui/passwords/manage_passwords_ui_controller.cc

Index: chrome/browser/ui/passwords/manage_passwords_ui_controller.cc
diff --git a/chrome/browser/ui/passwords/manage_passwords_ui_controller.cc b/chrome/browser/ui/passwords/manage_passwords_ui_controller.cc
index 7f44b422f408ba9b5ac4573354f48545f3d53e69..52694ee9f385bf57d84416f1ee60a7d95750d9a5 100644
--- a/chrome/browser/ui/passwords/manage_passwords_ui_controller.cc
+++ b/chrome/browser/ui/passwords/manage_passwords_ui_controller.cc
@@ -4,6 +4,7 @@
 
 #include "chrome/browser/ui/passwords/manage_passwords_ui_controller.h"
 
+#include "base/metrics/histogram_macros.h"
 #include "chrome/app/chrome_command_ids.h"
 #include "chrome/browser/browsing_data/browsing_data_helper.h"
 #include "chrome/browser/password_manager/chrome_password_manager_client.h"
@@ -112,6 +113,8 @@ void ManagePasswordsUIController::OnPasswordSubmitted(
   origin_ = PendingPassword().origin;
   SetState(password_manager::ui::PENDING_PASSWORD_AND_BUBBLE_STATE);
   timer_.reset(new base::ElapsedTimer());
+  UMA_HISTOGRAM_BOOLEAN("PasswordManager.OfferSaveEmptyUsername",

[vabr (Chromium), 2015/01/29 15:40:23]

You might consider putting this in PasswordManager::AskUserOrSavePassword, so
that it works also with the infobar and on mobile.

[vasilii, 2015/01/30 12:35:41]

Done.

+                        PendingPassword().username_value.empty());
   UpdateBubbleAndIconVisibility();
 }