Add metrics to printer setup flow.

chrome/browser/chromeos/printing/printer_configurer.h

 // Copyright 2017 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.
 
 #ifndef CHROME_BROWSER_CHROMEOS_PRINTING_PRINTER_CONFIGURER_H_
 #define CHROME_BROWSER_CHROMEOS_PRINTING_PRINTER_CONFIGURER_H_
 
 #include <memory>
 
 #include "base/callback_forward.h"
 #include "chromeos/printing/printer_configuration.h"
 
 class Profile;
 
 namespace chromeos {
 
+// These values are written to logs.  New enum values can be added, but existing
+// enums must never be renumbered or deleted and reused.
 enum PrinterSetupResult {
   kFatalError = 0,          // Setup failed in an unrecognized way
   kSuccess = 1,             // Printer set up successfully
   kPrinterUnreachable = 2,  // Could not reach printer
   kDbusError = 3,           // Could not contact debugd
   // Space left for additional errors
 
   // PPD errors
   kPpdTooLarge = 10,       // PPD exceeds size limit
   kInvalidPpd = 11,        // PPD rejected by cupstestppd
@@ skipping 22 matching lines @@
   virtual void SetUpPrinter(const Printer& printer,
                             const PrinterSetupCallback& callback) = 0;
 
  protected:
   PrinterConfigurer() = default;
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_PRINTING_PRINTER_CONFIGURER_H_