Check username validity in the FakeAuthPolicyClient

chrome/browser/resources/chromeos/login/offline_ad_login.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 Polymer element for displaying AD domain joining and AD
  * Authenticate user screens.
  */
 // Possible error states of the screen. Must be in the same order as
 // ActiveDirectoryErrorState enum values.
@@ skipping 106 matching lines @@
       case ACTIVE_DIRECTORY_ERROR_STATE.BAD_PASSWORD:
         this.$.passwordInput.isInvalid = true;
         break;
     }
   },
 
   /** @private */
   onSubmit_: function() {
     if (this.showMachineInput && !this.$.machineNameInput.checkValidity())
       return;
+    if (!this.$.userInput.checkValidity())
+      return;
     if (!this.$.passwordInput.checkValidity())
       return;
     var user = /** @type {string} */ (this.$.userInput.value);
     if (!user.includes('@') && this.userRealm)
       user += this.userRealm;
     var msg = {
       'machinename': this.$.machineNameInput.value,
       'username': user,
       'password': this.$.passwordInput.value
     };
     this.$.passwordInput.value = '';
     this.fire('authCompleted', msg);
   },
 });