Add back button to chrome://devices

chrome/browser/resources/local_discovery/local_discovery.js

 // Copyright 2013 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.
 
 /**
  * Javascript for local_discovery.html, served from chrome://devices/
  * This is used to show discoverable devices near the user as well as
  * cloud devices registered to them.
  *
  * The object defined in this javascript file listens for callbacks from the
@@ skipping 587 matching lines @@
       cloudDevicesLoginButtonClicked);
 
     $('register-login-button').addEventListener(
       'click',
       registerLoginButtonClicked);
 
     $('register-overlay-login-button').addEventListener(
       'click',
       registerOverlayLoginButtonClicked);
 
+    if (loadTimeData.valueExists('backButtonURL')) {
+      $('back-button').hidden = false;
+      $('back-button').addEventListener('click', function() {
+        window.location.href = loadTimeData.getString('backButtonURL');
+      });
+    }
+
     updateVisibility();
     document.addEventListener('visibilitychange', updateVisibility, false);
 
     focusManager = new LocalDiscoveryFocusManager();
     focusManager.initialize();
 
     chrome.send('start');
     recordUmaEvent(DEVICES_PAGE_EVENTS.OPENED);
   });
 
   return {
     onRegistrationSuccess: onRegistrationSuccess,
     onRegistrationFailed: onRegistrationFailed,
     onUnregisteredDeviceUpdate: onUnregisteredDeviceUpdate,
     onRegistrationConfirmedOnPrinter: onRegistrationConfirmedOnPrinter,
     onCloudDeviceListAvailable: onCloudDeviceListAvailable,
     onCloudDeviceListUnavailable: onCloudDeviceListUnavailable,
     onDeviceCacheFlushed: onDeviceCacheFlushed,
     onRegistrationCanceledPrinter: onRegistrationCanceledPrinter,
     onRegistrationTimeout: onRegistrationTimeout,
     setUserLoggedIn: setUserLoggedIn,
     setupCloudPrintConnectorSection: setupCloudPrintConnectorSection,
     removeCloudPrintConnectorSection: removeCloudPrintConnectorSection
   };
 });