update elements and fix some bugs

lib/paper_item.dart

 // DO NOT EDIT: auto-generated with `pub run custom_element_apigen:update`
 
 /// Dart API for the polymer element `paper_item`.
 @HtmlImport('paper_item_nodart.html')
 library polymer_elements.lib.src.paper_item.paper_item;
 
 import 'dart:html';
 import 'dart:js' show JsArray, JsObject;
 import 'package:web_components/web_components.dart';
 import 'package:polymer_interop/polymer_interop.dart';
 import 'iron_control_state.dart';
 import 'iron_button_state.dart';
 import 'iron_a11y_keys_behavior.dart';
 import 'paper_styles.dart';
 import 'paper_item_shared_styles.dart';
 
+/// Material design: [Lists](https://www.google.com/design/spec/components/lists.html)
+///
 /// `<paper-item>` is a non-interactive list item. By default, it is a horizontal flexbox.
 ///
 ///     <paper-item>Item</paper-item>
 ///
 /// Use this element with `<paper-item-body>` to make Material Design styled two-line and three-line
 /// items.
 ///
 ///     <paper-item>
 ///       <paper-item-body two-line>
 ///         <div>Show your status</div>
 ///         <div secondary>Your status is visible to everyone</div>
 ///       </paper-item-body>
 ///       <iron-icon icon="warning"></iron-icon>
 ///     </paper-item>
 ///
 /// ### Styling
 ///
 /// The following custom properties and mixins are available for styling:
 ///
-/// Custom property | Description | Default
-/// ----------------|-------------|----------
-/// `--paper-item-min-height` | Minimum height of the item | `48px`
-/// `--paper-item`            | Mixin applied to the item  | `{}`
+/// Custom property               | Description                                    | Default
+/// ------------------------------|------------------------------------------------|----------
+/// `--paper-item-min-height`     | Minimum height of the item                     | `48px`
+/// `--paper-item`                | Mixin applied to the item                      | `{}`
+/// `--paper-item-selected-weight`| The font weight of a selected item             | `bold`
+/// `--paper-item-selected`       | Mixin applied to selected paper-items                | `{}`
+/// `--paper-item-disabled-color` | The color for disabled paper-items             | `--disabled-text-color`
+/// `--paper-item-disabled`       | Mixin applied to disabled paper-items        | `{}`
+/// `--paper-item-focused`        | Mixin applied to focused paper-items         | `{}`
+/// `--paper-item-focused-before` | Mixin applied to :before focused paper-items | `{}`
+///
 ///
 /// ### Accessibility
 ///
 /// This element has `role="listitem"` by default. Depending on usage, it may be more appropriate to set
 /// `role="menuitem"`, `role="menuitemcheckbox"` or `role="menuitemradio"`.
 ///
 ///     <paper-item role="menuitemcheckbox">
 ///       <paper-item-body>
 ///         Show your status
 ///       </paper-item-body>
 ///       <paper-checkbox></paper-checkbox>
 ///     </paper-item>
 @CustomElementProxy('paper-item')
 class PaperItem extends HtmlElement with CustomElementProxyMixin, PolymerBase, IronControlState, IronA11yKeysBehavior, IronButtonState {
   PaperItem.created() : super.created();
   factory PaperItem() => new Element.tag('paper-item');
 }