update elements and fix some bugs

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

Index: lib/src/iron-list/test/x-list.html
diff --git a/lib/src/iron-list/test/x-list.html b/lib/src/iron-list/test/x-list.html
index b68e3c618ef5b959cf3f3649038a7c168baed4c0..e38ce2507deff62146d5bdbe0ea6c0f3c4912b35 100644
--- a/lib/src/iron-list/test/x-list.html
+++ b/lib/src/iron-list/test/x-list.html
@@ -39,7 +39,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
     <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>
@@ -64,6 +64,10 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
       listHeight: {
         type: Number,
         value: 300
+      },
+
+      pre: {
+        type: Boolean
       }
     },
 
@@ -71,12 +75,18 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
       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>