Change getExtensionPrinters to cr.sendWithPromise

chrome/browser/ui/webui/print_preview/print_preview_handler.h

Index: chrome/browser/ui/webui/print_preview/print_preview_handler.h
diff --git a/chrome/browser/ui/webui/print_preview/print_preview_handler.h b/chrome/browser/ui/webui/print_preview/print_preview_handler.h
index 8cee113c8d5ebff9e0c71274c87f41fda1d2f464..9d56123af51e1fd46e0fac89269457577b76ca75 100644
--- a/chrome/browser/ui/webui/print_preview/print_preview_handler.h
+++ b/chrome/browser/ui/webui/print_preview/print_preview_handler.h
@@ -320,10 +320,14 @@ class PrintPreviewHandler
   void EnsureExtensionPrinterHandlerSet();
 
   // Called when a list of printers is reported by an extension.
+  // |callback_id|: The javascript callback to call if all extension printers
+  //     are loaded (i.e. |done| = true)
   // |printers|: The list of printers managed by the extension.
   // |done|: Whether all the extensions have reported the list of printers
   //     they manage.
-  void OnGotPrintersForExtension(const base::ListValue& printers, bool done);
+  void OnGotPrintersForExtension(const std::string& callback_id,
+                                 const base::ListValue& printers,
+                                 bool done);
 
   // Called when an extension reports information requested for a provisional
   // printer.