Roll Polymer from 1.5.0 -> 1.6.0 to pick up native CSS custom props

third_party/polymer/v1_0/components-chromium/iron-checked-element-behavior/iron-checked-element-behavior-extracted.js

 /**
    * Use `Polymer.IronCheckedElementBehavior` to implement a custom element
    * that has a `checked` property, which can be used for validation if the
    * element is also `required`. Element instances implementing this behavior
    * will also be registered for use in an `iron-form` element.
    *
    * @demo demo/index.html
    * @polymerBehavior Polymer.IronCheckedElementBehavior
    */
   Polymer.IronCheckedElementBehaviorImpl = {
@@ skipping 41 matching lines @@
     created: function() {
       // Used by `iron-form` to handle the case that an element with this behavior
       // doesn't have a role of 'checkbox' or 'radio', but should still only be
       // included when the form is serialized if `this.checked === true`.
       this._hasIronCheckedElementBehavior = true;
     },
 
     /**
      * Returns false if the element is required and not checked, and true otherwise.
      * @param {*=} _value Ignored.
-     * @return {boolean} true if `required` is false, or if `required` and `checked` are both true.
+     * @return {boolean} true if `required` is false or if `checked` is true.
      */
     _getValidity: function(_value) {
-      return this.disabled || !this.required || (this.required && this.checked);
+      return this.disabled || !this.required || this.checked;
     },
 
     /**
      * Update the aria-required label when `required` is changed.
      */
     _requiredChanged: function() {
       if (this.required) {
         this.setAttribute('aria-required', 'true');
       } else {
         this.removeAttribute('aria-required');
@@ skipping 17 matching lines @@
       }
     }
   };
 
   /** @polymerBehavior Polymer.IronCheckedElementBehavior */
   Polymer.IronCheckedElementBehavior = [
     Polymer.IronFormElementBehavior,
     Polymer.IronValidatableBehavior,
     Polymer.IronCheckedElementBehaviorImpl
   ];