update elements and fix some bugs

lib/paper_material.dart

 // DO NOT EDIT: auto-generated with `pub run custom_element_apigen:update`
 
 /// Dart API for the polymer element `paper_material`.
 @HtmlImport('paper_material_nodart.html')
 library polymer_elements.lib.src.paper_material.paper_material;
 
 import 'dart:html';
 import 'dart:js' show JsArray, JsObject;
 import 'package:web_components/web_components.dart';
 import 'package:polymer_interop/polymer_interop.dart';
 import 'shadow.dart';
 
+/// Material design: [Cards](https://www.google.com/design/spec/components/cards.html)
+///
 /// `paper-material` is a container that renders two shadows on top of each other to
 /// create the effect of a lifted piece of paper.
 ///
 /// Example:
 ///
 ///     <paper-material elevation="1">
 ///       ... content ...
 ///     </paper-material>
 @CustomElementProxy('paper-material')
 class PaperMaterial extends HtmlElement with CustomElementProxyMixin, PolymerBase {
   PaperMaterial.created() : super.created();
   factory PaperMaterial() => new Element.tag('paper-material');
 
   /// Set this to true to animate the shadow when setting a new
   /// `elevation` value.
   bool get animated => jsElement[r'animated'];
   set animated(bool value) { jsElement[r'animated'] = value; }
 
   /// The z-depth of this element, from 0-5. Setting to 0 will remove the
   /// shadow, and each increasing number greater than 0 will be "deeper"
   /// than the last.
   num get elevation => jsElement[r'elevation'];
   set elevation(num value) { jsElement[r'elevation'] = value; }
 }