Polymer notifications are not forwarded for scopeless nodes

[tomalec]

Steps to reproduce

1. Create imported-template using <dom-bind>

   <dom-bind id="domBind">
     <imported-template html="{{html}}" model="{{model}}"></imported-template>
   </dom-bind>

2. Attach a model domBind.set('model', {foo: 'not changed'}); and import scopeless document:

   <template><dom-bind>{{model.foo}}</dom-bind></template>

3. Change foo property of a model using `domBind.set('model.foo', 'changed');

Live Demo

https://jsbin.com/nufinevija/1/edit?html,output

Expected result

Inner dom-bind should get notified and value changed

Actual result

dom-bind is not notified and value is not changed

Browsers affected

• Chrome
• Firefox
• Edge
• Safari 9
• Safari 8
• IE 11

//cc @alshakero