Roll third_party/polymer.

third_party/polymer/v1_0/components-chromium/iron-selector/iron-selectable-extracted.js

 /** @polymerBehavior */
   Polymer.IronSelectableBehavior = {
 
       /**
        * Fired when iron-selector is activated (selected or deselected).
        * It is fired before the selected items are changed.
        * Cancel the event to abort selection.
        *
        * @event iron-activate
        */
@@ skipping 14 matching lines @@
        * Fired when the list of selectable items changes (e.g., items are
        * added or removed). The detail of the event is a list of mutation
        * records that describe what changed.
        *
        * @event iron-items-changed
        */
 
     properties: {
 
       /**
-       * If you want to use the attribute value of an element for `selected` instead of the index,
-       * set this to the name of the attribute.
+       * If you want to use an attribute value or property of an element for
+       * `selected` instead of the index, set this to the name of the attribute
+       * or property. Hyphenated values are converted to camel case when used to
+       * look up the property of a selectable element. Camel cased values are
+       * *not* converted to hyphenated values for attribute lookup. It's
+       * recommended that you provide the hyphenated form of the name so that
+       * selection works in both cases. (Use `attr-or-property-name` instead of
+       * `attrOrPropertyName`.)
        */
       attrForSelected: {
         type: String,
         value: null
       },
 
       /**
        * Gets or sets the selected element. The default is to use the index of the item.
        * @type {string|number}
        */
@@ skipping 220 matching lines @@
         var item = this.items[index];
         if (item) {
           return this._valueForItem(item);
         }
       } else {
         return index;
       }
     },
 
     _valueForItem: function(item) {
-      var propValue = item[this.attrForSelected];
+      var propValue = item[Polymer.CaseMap.dashToCamelCase(this.attrForSelected)];
       return propValue != undefined ? propValue : item.getAttribute(this.attrForSelected);
     },
 
     _applySelection: function(item, isSelected) {
       if (this.selectedClass) {
         this.toggleClass(this.selectedClass, isSelected, item);
       }
       if (this.selectedAttribute) {
         this.toggleAttribute(this.selectedAttribute, isSelected, item);
       }
@@ skipping 38 matching lines @@
     },
 
     _itemActivate: function(value, item) {
       if (!this.fire('iron-activate',
           {selected: value, item: item}, {cancelable: true}).defaultPrevented) {
         this.select(value);
       }
     }
 
   };