update elements and fix some bugs

lib/src/iron-list/test/x-list.html

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@@ skipping 21 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>
 
 <script>
   Polymer({
     is: 'x-list',
 
     properties: {
       data: {
         type: Array
       },
 
       itemHeight: {
         type: Number,
         value: 100
       },
 
       listHeight: {
         type: Number,
         value: 300
+      },
+
+      pre: {
+        type: Boolean
       }
     },
 
     get list() {
       return this.$.list;
     },
 
-    _computedItemHeight: function() {
-      return 'height: ' + (this.itemHeight) + 'px';
+    _computedItemHeight: function(item) {
+      var css = this.pre ? 'white-space:pre;' : '';
+      if (item.height) {
+        css += this.itemHeight === 0 ? '' : 'height: ' + (item.height) + 'px;';
+      } else if (this.itemHeight) {
+        css += 'height: ' + (this.itemHeight) + 'px;';
+      }
+      return css;
     },
 
     _computedListHeight: function(listHeight) {
       return 'height: ' + (listHeight) + 'px';
-    },
+    }
   });
 </script>