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

chrome/browser/resources/settings/printing_page/cups_printers_browser_proxy.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 A helper object used from the "CUPS printing" section to
  * interact with the browser.
  */
 
 /**
@@ skipping 44 matching lines @@
 
     /**
      * @return {!Promise<string>} The full path of the printer PPD file.
      */
     getCupsPrinterPPDPath: function() {},
 
     /**
      * @param {!CupsPrinterInfo} newPrinter
      */
     addCupsPrinter: function(newPrinter) {},
+
+    startDiscoveringPrinters: function() {},
+
+    stopDiscoveringPrinters: function() {},
   };
 
   /**
    * @constructor
    * @implements {settings.CupsPrintersBrowserProxy}
    */
   function CupsPrintersBrowserProxyImpl() {}
   cr.addSingletonGetter(CupsPrintersBrowserProxyImpl);
 
   CupsPrintersBrowserProxyImpl.prototype = {
@@ skipping 14 matching lines @@
 
     /** @override */
     addCupsPrinter: function(newPrinter) {
       chrome.send('addCupsPrinter', [newPrinter]);
     },
 
     /** @override */
     getCupsPrinterPPDPath: function() {
       return cr.sendWithPromise('selectPPDFile');
     },
+
+    /** @override */
+    startDiscoveringPrinters: function() {
+      chrome.send('startDiscoveringPrinters');
+    },
+
+    /** @override */
+    stopDiscoveringPrinters: function() {
+      chrome.send('stopDiscoveringPrinters');
+    },
   };
 
   return {
     CupsPrintersBrowserProxy: CupsPrintersBrowserProxy,
     CupsPrintersBrowserProxyImpl: CupsPrintersBrowserProxyImpl,
   };
 });