Fixes #3270.

src/lib/base.html

@@ -33,7 +33,6 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
 
     createdCallback: function() {
       Polymer.telemetry.instanceCount++;
-      this.isAttached = false;
       this.root = this;
       this._doBehavior('created'); // abstract
       this._initFeatures(); // abstract

test/unit/bind-elements.html

@@ -468,3 +468,23 @@
     <input id="input" value$="{{inputValue}}">
   </template>
 </dom-module>
+
+
+<dom-module id="x-bind-is-attached">
+  <template>
+    <div id="check">{{isAttached}}</div>
+  </template>
+  <script>
+    Polymer({
+      is: 'x-bind-is-attached',
+      properties: {
+        isAttached: {
+          observer: '_isAttachedChanged'
+        }
+      },
+      _isAttachedChanged: function() {}
+    });
+  </script>
+</dom-module>
+
+<s

test/unit/bind.html

@@ -719,6 +719,15 @@ suite('binding corner cases', function() {
     assert.equal(el.$.binding.textContent, 'binding');
   });
 
+  test('bind to isAttached', function() {
+    var el = document.createElement('x-bind-is-attached');
+    sinon.spy(el, '_isAttachedChanged');
+    document.body.appendChild(el);
+    Polymer.dom.flush();
+    assert.equal(el.$.check.textContent, 'true');
+    assert.isTrue(el._isAttachedChanged.calledOnce);
+    document.body.removeChild(el);
+  });
 });
 
 suite('compound binding / string interpolation', function() {