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

chrome/service/cloud_print/print_system_win.cc

Index: chrome/service/cloud_print/print_system_win.cc
===================================================================
--- chrome/service/cloud_print/print_system_win.cc	(revision 72357)
+++ chrome/service/cloud_print/print_system_win.cc	(working copy)
@@ -250,7 +250,8 @@
   // PrintSystem implementation.
   virtual PrintSystemResult Init();
 
-  virtual void EnumeratePrinters(printing::PrinterList* printer_list);
+  virtual PrintSystem::PrintSystemResult EnumeratePrinters(
+      printing::PrinterList* printer_list);
 
   virtual void GetPrinterCapsAndDefaults(
       const std::string& printer_name,
@@ -605,8 +606,10 @@
   return PrintSystemResult(true, std::string());
 }
 
-void PrintSystemWin::EnumeratePrinters(printing::PrinterList* printer_list) {
-  print_backend_->EnumeratePrinters(printer_list);
+PrintSystem::PrintSystemResult PrintSystemWin::EnumeratePrinters(
+    printing::PrinterList* printer_list) {
+  bool ret = print_backend_->EnumeratePrinters(printer_list);
+  return PrintSystemResult(ret, std::string());
 }
 
 void PrintSystemWin::GetPrinterCapsAndDefaults(