update elements and fix some bugs

test/fixtures/x_list.html

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 <dom-module id="x-list">
@@ skipping 17 matching lines @@
     .item:nth-child(even) {
       background-color: red;
     }
   </style>
 
   <template>
     <iron-list style$="[[computedListHeight(listHeight)]]" items="[[data]]"
                as="item" id="list">
       <template>
         <div class="item">
-          <div style$="[[computedItemHeight()]]">[[item.index]]</div>
+          <div style$="[[computedItemHeight(item)]]">[[item.index]]</div>
         </div>
       </template>
     </iron-list>
   </template>
 
 </dom-module>