[CUPS] Implement the Webui handler for the printers auto discovery.

chrome/browser/resources/settings/printing_page/cups_printers.js

 // Copyright 2016 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.
 
 /**
  * @fileoverview 'settings-cups-printers' is a component for showing CUPS
  * Printer settings subpage (chrome://md-settings/cupsPrinters). It is used to
  * set up legacy & non-CloudPrint printers on ChromeOS by leveraging CUPS (the
  * unix printing system) and the many open source drivers built for CUPS.
  */
@@ skipping 20 matching lines @@
     this.updateCupsPrintersList_();
     this.addWebUIListener('on-add-cups-printer', this.onAddPrinter_.bind(this));
   },
 
   /**
    * @param {boolean} success
    * @param {string} printerName
    * @private
    */
   onAddPrinter_: function(success, printerName) {
-    if (!success)
-      return;
-
-    this.updateCupsPrintersList_();
-    var message = this.$.addPrinterMessage;
-    message.textContent = loadTimeData.getStringF(
-        'printerAddedSuccessfulMessage', printerName);
+    if (success) {
+      this.updateCupsPrintersList_();
+      var message = this.$.addPrinterDoneMessage;
+      message.textContent = loadTimeData.getStringF(
+          'printerAddedSuccessfulMessage', printerName);
+    } else {
+      var message = this.$.addPrinterErrorMessage;
+    }
     message.hidden = false;
     window.setTimeout(function() {
       message.hidden = true;
     }, 3000);
   },
 
   /** @private */
   updateCupsPrintersList_: function() {
     settings.CupsPrintersBrowserProxyImpl.getInstance().
         getCupsPrintersList().then(this.printersChanged_.bind(this));
   },
 
   /**
    * @param {!CupsPrintersList} cupsPrintersList
    * @private
    */
   printersChanged_: function(cupsPrintersList) {
     this.printers = cupsPrintersList.printerList;
   },
 
   /** @private */
   onAddPrinterTap_: function() {
     this.$.addPrinterDialog.open();
+    this.$.addPrinterErrorMessage.hidden = true;
   },
 });