Roll third_party/polymer.

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

Index: third_party/polymer/v1_0/components-chromium/iron-selector/iron-selectable-extracted.js
diff --git a/third_party/polymer/v1_0/components-chromium/iron-selector/iron-selectable-extracted.js b/third_party/polymer/v1_0/components-chromium/iron-selector/iron-selectable-extracted.js
index 291e7de4c4758e36029e74eda4d0d0c39eabbc7e..09ee6c5084432194e2f1ff67a6002afbf429c931 100644
--- a/third_party/polymer/v1_0/components-chromium/iron-selector/iron-selectable-extracted.js
+++ b/third_party/polymer/v1_0/components-chromium/iron-selector/iron-selectable-extracted.js
@@ -32,8 +32,14 @@
     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,
@@ -274,7 +280,7 @@
     },
 
     _valueForItem: function(item) {
-      var propValue = item[this.attrForSelected];
+      var propValue = item[Polymer.CaseMap.dashToCamelCase(this.attrForSelected)];
       return propValue != undefined ? propValue : item.getAttribute(this.attrForSelected);
     },