Import Polymer 0.8 and several key elements.

third_party/polymer/v0_8/components/polymer/src/micro/constructor.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>
+
+  /**
+   * Generates a boilerplate constructor.
+   * 
+   *     XFoo = Polymer({
+   *       is: 'x-foo'
+   *     });
+   *     ASSERT(new XFoo() instanceof XFoo);
+   *  
+   * You can supply a custom constructor on the prototype. But remember that 
+   * this constructor will only run if invoked **manually**. Elements created
+   * via `document.createElement` or from HTML _will not invoke this method_.
+   * 
+   * Instead, we reuse the concept of `constructor` for a factory method which 
+   * can take arguments. 
+   * 
+   *     MyFoo = Polymer({
+   *       is: 'my-foo',
+   *       constructor: function(foo) {
+   *         this.foo = foo;
+   *       }
+   *       ...
+   *     });
+   * 
+   * @class base feature: constructor
+   */
+
+  Polymer.Base._addFeature({
+
+    // registration-time
+
+    _prepConstructor: function() {
+      // support both possible `createElement` signatures
+      this._factoryArgs = this.extends ? [this.extends, this.is] : [this.is];
+      // thunk the constructor to delegate allocation to `createElement`
+      var ctor = function() { 
+        return this._factory(arguments); 
+      };
+      if (this.hasOwnProperty('extends')) {
+        ctor.extends = this.extends; 
+      }
+      // ensure constructor is set. The `constructor` property is
+      // not writable on Safari; note: Chrome requires the property
+      // to be configurable.
+      Object.defineProperty(this, 'constructor', {value: ctor, 
+        writable: true, configurable: true});
+      ctor.prototype = this;
+    },
+
+    _factory: function(args) {
+      var elt = document.createElement.apply(document, this._factoryArgs);
+      if (this.factoryImpl) {
+        this.factoryImpl.apply(elt, args);
+      }
+      return elt;
+    }
+
+  });
+
+</script>