title: Changes don't appear to fire for computed bindings
body: <p>If I create an observer for all changes on a structure object, the observer will get called unless the the binding is a change to a value in a computed binding.</p>
  
  <p>Is this the expected behavior? If so, how can I capture changes to the property in the computed binding?</p>
  
  <p>Example:</p>
  
  <pre><code>&lt;link rel="import" href="../../bower_components/paper-input/paper-input.html"&gt;
  &lt;dom-module id="binding-test"&gt;
  
  &lt;template&gt;
      &lt;paper-input label="Not computed" value="{{myObject.prop1}}"&gt;&lt;/paper-input&gt;
      &lt;paper-input label="Computed" value="{{computeIt(myObject.prop2)}}"&gt;&lt;/paper-input&gt;
  &lt;/template&gt;
  
  &lt;script&gt;
      Polymer({
          is:"binding-test",
  
          properties: {
              myObject: {
                  type: Object,
                  notify: true,
                  value: {
                      prop1: 1,
                      prop2: 2
                  }
              }
          },
  
          observers: [
              'somethingChanged(myObject.*)'
          ],
  
          somethingChanged: function(changeRecord) {
              // This code is never executed when the Computed input field is changed
              console.log(changeRecord);
          },
  
          computeIt: function(value) {
              return value;
          }
      });
  &lt;/script&gt;
  &lt;/dom-module&gt;
  </code></pre>