Update bower.json for Polymer elements and add PRESUBMIT.py

third_party/polymer/v1_0/components/paper-radio-button/paper-radio-button.html

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 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
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 <link rel="import" href="../polymer/polymer.html">
 <link rel="import" href="../paper-ripple/paper-ripple.html">
 <link rel="import" href="../paper-styles/default-theme.html">
 <link rel="import" href="../paper-behaviors/paper-inky-focus-behavior.html">
 
 <!--
 `paper-radio-button` is a button that can be either checked or unchecked.
-User can tap the radio button to check it.  But it cannot be unchecked by
-tapping once checked.
+User can tap the radio button to check or uncheck it.
 
-Use `paper-radio-group` to group a set of radio buttons.  When radio buttons
-are inside a radio group, only one radio button in the group can be checked.
+Use a `<paper-radio-group>` to group a set of radio buttons.  When radio buttons
+are inside a radio group, exactly one radio button in the group can be checked
+at any time.
 
 Example:
 
     <paper-radio-button></paper-radio-button>
+    <paper-radio-button>Item label</paper-radio-button>
 
 ### Styling
 
 The following custom properties and mixins are available for styling:
 
 Custom property | Description | Default
 ----------------|-------------|----------
+`--paper-radio-button-unchecked-background-color` | Radio button background color when the input is not checked | `transparent`
 `--paper-radio-button-unchecked-color` | Radio button color when the input is not checked | `--primary-text-color`
 `--paper-radio-button-unchecked-ink-color` | Selected/focus ripple color when the input is not checked | `--primary-text-color`
 `--paper-radio-button-checked-color` | Radio button color when the input is checked | `--default-primary-color`
 `--paper-radio-button-checked-ink-color` | Selected/focus ripple color when the input is checked | `--default-primary-color`
 `--paper-radio-button-label-color` | Label color | `--primary-text-color`
 
 @group Paper Elements
 @element paper-radio-button
 @hero hero.svg
 @demo demo/index.html
@@ skipping 84 matching lines @@
 
       _checkedChanged: function() {
         this.setAttribute('aria-checked', this.checked ? 'true' : 'false');
         this.active = this.checked;
         this.fire('iron-change');
       }
     })
   </script>
 
 </dom-module>