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

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

Index: chrome/browser/resources/settings/printing_page/cups_printers_browser_proxy.js
diff --git a/chrome/browser/resources/settings/printing_page/cups_printers_browser_proxy.js b/chrome/browser/resources/settings/printing_page/cups_printers_browser_proxy.js
index 3b4e4e24b326df715866d08787def2f53b723ba3..d9dd97ad594e282aad8ff11af44e34ee3b486e0c 100644
--- a/chrome/browser/resources/settings/printing_page/cups_printers_browser_proxy.js
+++ b/chrome/browser/resources/settings/printing_page/cups_printers_browser_proxy.js
@@ -62,6 +62,10 @@ cr.define('settings', function() {
      * @param {!CupsPrinterInfo} newPrinter
      */
     addCupsPrinter: function(newPrinter) {},
+
+    startDiscoveringPrinters: function() {},
+
+    stopDiscoveringPrinters: function() {},
   };
 
   /**
@@ -96,6 +100,16 @@ cr.define('settings', function() {
     getCupsPrinterPPDPath: function() {
       return cr.sendWithPromise('selectPPDFile');
     },
+
+    /** @override */
+    startDiscoveringPrinters: function() {
+      chrome.send('startDiscoveringPrinters');
+    },
+
+    /** @override */
+    stopDiscoveringPrinters: function() {
+      chrome.send('stopDiscoveringPrinters');
+    },
   };
 
   return {