Update to use one less proxy per element

test/src/common/polymer_mixin_test.html

Index: test/src/common/polymer_mixin_test.html
diff --git a/test/src/common/polymer_mixin_test.html b/test/src/common/polymer_mixin_test.html
index aa7f9c9e6e25764214df29b730dbc5b1e1397424..93c86c80c57e945119c499e81a54ff1819ee0d98 100644
--- a/test/src/common/polymer_mixin_test.html
+++ b/test/src/common/polymer_mixin_test.html
@@ -20,6 +20,16 @@ BSD-style license that can be found in the LICENSE file.
           child
         </div>
       </div>
+      <!-- This test makes sure that if a list is in a binding the updates
+          don't happen twice -->
+      <sub-element id="sub" my-ints="{{myInts}}" my-map="{{myMap}}"
+          my-model="{{myModel}}"></sub-element>
+    </template>
+  </dom-module>
+
+  <dom-module id="sub-element">
+    <template>
+      <span id="modelValue">{{myModel.value}}</span>
     </template>
   </dom-module>
 </body>