Add Printing.CUPS.PrintersDiscovered to our metrics.

chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc

 // Copyright 2016 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 "chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/files/file_util.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/memory/ptr_util.h"
+#include "base/metrics/histogram_macros.h"
 #include "base/path_service.h"
 #include "base/strings/string_util.h"
 #include "base/threading/sequenced_task_runner_handle.h"
 #include "base/values.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chromeos/printing/ppd_provider_factory.h"
 #include "chrome/browser/chromeos/printing/printer_configurer.h"
 #include "chrome/browser/chromeos/printing/printer_discoverer.h"
 #include "chrome/browser/chromeos/printing/printers_manager_factory.h"
 #include "chrome/browser/download/download_prefs.h"
@@ skipping 379 matching lines @@
     const std::vector<Printer>& printers) {
   std::unique_ptr<base::ListValue> printers_list =
       base::MakeUnique<base::ListValue>();
   for (const auto& printer : printers) {
     printers_list->Append(GetPrinterInfo(printer));
   }
 
   FireWebUIListener("on-printer-discovered", *printers_list);
 }
 
-void CupsPrintersHandler::OnDiscoveryInitialScanDone() {
+void CupsPrintersHandler::OnDiscoveryInitialScanDone(int printer_count) {
+  UMA_HISTOGRAM_COUNTS_100("Printing.CUPS.PrintersDiscovered", printer_count);
   FireWebUIListener("on-printer-discovery-done");
 }
 
 }  // namespace settings
 }  // namespace chromeos