MD Settings: Users: Fix add person validation and dialog focus

chrome/browser/resources/settings/people_page/users_add_user_dialog.js

Index: chrome/browser/resources/settings/people_page/users_add_user_dialog.js
diff --git a/chrome/browser/resources/settings/people_page/users_add_user_dialog.js b/chrome/browser/resources/settings/people_page/users_add_user_dialog.js
index b1383ee9516280b2881e0e9f6cc00562bc85b9ab..99b274881848129cce5a173c2f5b6b0151ee6c46 100644
--- a/chrome/browser/resources/settings/people_page/users_add_user_dialog.js
+++ b/chrome/browser/resources/settings/people_page/users_add_user_dialog.js
@@ -32,7 +32,16 @@ var EMAIL_REGEX = new RegExp(
 Polymer({
   is: 'settings-users-add-user-dialog',
 
+  properties: {
+    /** @private */
+    isValid_: {
+      type: Boolean,
+      value: false,
+    },
+  },
+
   open: function() {
+    this.isValid_ = false;
     this.$.dialog.showModal();
   },
 
@@ -48,11 +57,8 @@ Polymer({
    */
   validate_: function() {
     var input = this.$.addUserInput.value;
-    var valid = NAME_ONLY_REGEX.test(input) || EMAIL_REGEX.test(input);
-
-    this.$.add.disabled = !valid;
-    this.$.addUserInput.invalid = !valid;
-    return valid;
+    this.isValid_ = NAME_ONLY_REGEX.test(input) || EMAIL_REGEX.test(input);
+    return this.isValid_;
   },
 
   /** @private */