Import Polymer 0.8 and several key elements.

third_party/polymer/v0_8/components/polymer/src/micro/extends.html

+<!--
+@license
+Copyright (c) 2014 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
+-->
+<script>
+
+  /**
+   * Support `extends` property (for type-extension only).
+   *
+   * If the mixin is String-valued, the corresponding Polymer module
+   * is mixed in.
+   *
+   *     Polymer({
+   *       is: 'pro-input',
+   *       extends: 'input',
+   *       ...
+   *     });
+   * 
+   * Type-extension objects are created using `is` notation in HTML, or via
+   * the secondary argument to `document.createElement` (the type-extension
+   * rules are part of the Custom Elements specification, not something 
+   * created by Polymer). 
+   * 
+   * Example:
+   * 
+   *     <!-- right: creates a pro-input element -->
+   *     <input is="pro-input">
+   *   
+   *     <!-- wrong: creates an unknown element -->
+   *     <pro-input>  
+   * 
+   *     <script>
+   *        // right: creates a pro-input element
+   *        var elt = document.createElement('input', 'pro-input');
+   * 
+   *        // wrong: creates an unknown element
+   *        var elt = document.createElement('pro-input');
+   *     <\script>
+   *
+   *   @class base feature: extends
+   */
+
+  Polymer.Base._addFeature({
+
+    _prepExtends: function() {
+      if (this.extends) {
+        this.__proto__ = this.getExtendedPrototype(this.extends);
+      }
+    },
+
+    getExtendedPrototype: function(tag) {
+      return this.getExtendedNativePrototype(tag);
+    },
+
+    nativePrototypes: {}, // static
+
+    getExtendedNativePrototype: function(tag) {
+      var p = this.nativePrototypes[tag];
+      if (!p) {
+        var np = this.getNativePrototype(tag);
+        p = this.extend(Object.create(np), Polymer.Base);
+        this.nativePrototypes[tag] = p;
+      }
+      return p;
+    },
+
+    getNativePrototype: function(tag) {
+      // TODO(sjmiles): sad necessity
+      return Object.getPrototypeOf(document.createElement(tag));
+    }
+
+  });
+
+</script>