Added a diagnostic user message when enumerating printers fails. Also tweaked...

chrome/service/cloud_print/print_system.h

 // Copyright (c) 2010 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_SERVICE_CLOUD_PRINT_PRINT_SYSTEM_H_
 #define CHROME_SERVICE_CLOUD_PRINT_PRINT_SYSTEM_H_
 #pragma once
 
 #include <map>
 #include <string>
@@ skipping 140 matching lines @@
       const printing::PrinterCapsAndDefaults&>::Type
           PrinterCapsAndDefaultsCallback;
 
   virtual ~PrintSystem();
 
   // Initialize print system. This need to be called before any other function
   // of PrintSystem.
   virtual PrintSystemResult Init() = 0;
 
   // Enumerates the list of installed local and network printers.
-  virtual void EnumeratePrinters(printing::PrinterList* printer_list) = 0;
+  virtual PrintSystemResult EnumeratePrinters(
+      printing::PrinterList* printer_list) = 0;
 
   // Gets the capabilities and defaults for a specific printer asynchronously.
   virtual void GetPrinterCapsAndDefaults(
       const std::string& printer_name,
       PrinterCapsAndDefaultsCallback* callback) = 0;
 
   // Returns true if printer_name points to a valid printer.
   virtual bool IsValidPrinter(const std::string& printer_name) = 0;
 
   // Returns true if ticket is valid.
@@ skipping 27 matching lines @@
 // Visual Studio where it gets confused between multiple Delegate
 // classes and gives a C2500 error. (I saw this error on the try bots -
 // the workaround was not needed for my machine).
 typedef PrintSystem::PrintServerWatcher::Delegate PrintServerWatcherDelegate;
 typedef PrintSystem::PrinterWatcher::Delegate PrinterWatcherDelegate;
 typedef PrintSystem::JobSpooler::Delegate JobSpoolerDelegate;
 
 }  // namespace cloud_print
 
 #endif  // CHROME_SERVICE_CLOUD_PRINT_PRINT_SYSTEM_H_