[third_party] add polymer 1.2.3

polymer_1.2.3/bower_components/iron-form-element-behavior/demo/simple-form.html

 <!--
 @license
 Copyright (c) 2015 The Polymer Project Authors. All rights reserved.
 This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
 The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
 The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
 Code distributed by Google as part of the polymer project is also
 subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
 -->
 <link rel="import" href="../../polymer/polymer.html">
 
 <script>
 
   Polymer({
 
     is: 'simple-form',
 
     extends: 'form',
 
     properties: {
       formElements: {
         type: Object,
         notify: true
       }
     },
 
     listeners: {
-      'iron-form-element-register': '_elementRegistered'
+      'iron-form-element-register': '_elementRegistered',
+      'iron-form-element-unregister': '_elementUnregistered'
     },
 
     ready: function() {
       this.formElements = [];
     },
 
     _elementRegistered: function(e) {
       this.formElements.push(e.target);
-      this.fire('element-registered');
+      e.target._parentForm = this;
+    },
+
+    _elementUnregistered: function(e) {
+      var target = e.detail.target;
+      if (target) {
+        var index = this.formElements.indexOf(target);
+        if (index > -1) {
+          this.formElements.splice(index, 1);
+        }
+      }
     }
 
   });
 
 </script>