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

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

Index: chrome/browser/resources/settings/people_page/users_add_user_dialog.html
diff --git a/chrome/browser/resources/settings/people_page/users_add_user_dialog.html b/chrome/browser/resources/settings/people_page/users_add_user_dialog.html
index 6d812fe8da42d04d4b6a8bdf589faeac87207528..69cd20b555f614d515cc6305c2cb010c6e3c45df 100644
--- a/chrome/browser/resources/settings/people_page/users_add_user_dialog.html
+++ b/chrome/browser/resources/settings/people_page/users_add_user_dialog.html
@@ -20,13 +20,15 @@
       <div class="title">$i18n{addUsers}</div>
       <div class="body">
         <paper-input id="addUserInput" label="$i18n{addUsersEmail}" autofocus
-            on-input="validate_">
+            on-input="validate_" invalid="[[!isValid_]]">
         </paper-input>
       </div>
       <div class="button-container">
-        <paper-button class="cancel-button" on-tap="onCancelTap_"
-            id="cancel">$i18n{cancel}</paper-button>
-        <paper-button id="add" on-tap="addUser_" class="action-button" disabled>
+        <paper-button class="cancel-button" on-tap="onCancelTap_">
+          $i18n{cancel}
+        </paper-button>
+        <paper-button on-tap="addUser_" class="action-button"
+            disabled$="[[!isValid_]]">

[dpapad, 2017/04/11 00:03:55]

Probably "$=" not needed here, "=" should be sufficient.

[stevenjb, 2017/04/11 00:44:22]

Either works, Polymer maps it to an attribute, and we use a mix in Settings. I
guess the advantage of $ is that it can be used as an attribute in CSS also.

           $i18n{add}
         </paper-button>
       </div>