Fix detached callback and add isAttached to SkyElements.

sky/tests/framework/templates.sky

 <sky>
 <import src="/sky/tests//resources/chai.sky" />
 <import src="/sky/tests/resources/mocha.sky" />
 <import src="/sky/tests/resources/test-element.sky" as="TestElement" />
 
 <div id="sandbox"></div>
 
 <script>
 describe("SkyElement templates", function() {
   var element;
   var sandbox = document.getElementById("sandbox");
 
   beforeEach(function() {
     element = new TestElement();
   });
   afterEach(function() {
     element.remove();
   });
 
   it("should stamp when the element is inserted", function() {
     assert.isNull(element.shadowRoot);
     sandbox.appendChild(element);
     assert.instanceOf(element.shadowRoot, ShadowRoot);
     assert.ok(element.shadowRoot.getElementById("inside"));
   });
 
+  it("should update isAttached when inserting", function() {
+    assert.isFalse(element.isAttached);
+    sandbox.appendChild(element);
+    assert.isTrue(element.isAttached);
+    element.remove();
+    assert.isFalse(element.isAttached);
+  });
+
   it("should connect data binding", function(done) {
     sandbox.appendChild(element);
     var inside = element.shadowRoot.getElementById("inside");
     Promise.resolve().then(function() {
       assert.equal(inside.textContent, 10);
       assert.equal(inside.attr, 10);
       element.value = 20;
     }).then(function() {
       assert.equal(inside.textContent, 20);
       assert.equal(inside.attr, 20);
@@ skipping 17 matching lines @@
     assert.equal(element.shadowRootReadyCount, 0);
     sandbox.appendChild(element);
     assert.equal(element.shadowRootReadyCount, 1);
     element.remove();
     sandbox.appendChild(element);
     assert.equal(element.shadowRootReadyCount, 1);
   });
 });
 </script>
 </sky>