Add Printing.CUPS.PrintersDiscovered to our metrics.

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

Index: chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc
diff --git a/chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc b/chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc
index 28a1781f5cad216bd1123cd274008f7d44ca2c0e..730e2e3f93ef61e319c9aae0f17edad81a4ff368 100644
--- a/chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc
+++ b/chrome/browser/ui/webui/settings/chromeos/cups_printers_handler.cc
@@ -11,6 +11,7 @@
 #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"
@@ -410,7 +411,8 @@ void CupsPrintersHandler::OnPrintersFound(
   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");
 }