Add two way data binding.

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>
 
 <test-element id="parser-element" checked="true" size="10" name="foo bar" />
 
 <script>
@@ skipping 113 matching lines @@
       element.value = 20;
     }).then(function() {
       assert.equal(inside.textContent, 20);
       assert.equal(inside.lang, 20);
       done();
     }).catch(function(e) {
       done(e);
     });
   });
 
+  it("should two way bind attributes", function(done) {
+    sandbox.appendChild(element);
+    var checkbox = element.shadowRoot.getElementById("checkbox");
+    assert.isFalse(checkbox.checked);
+    assert.isFalse(element.checked);
+    element.checked = true;
+    assert.isTrue(element.checked);
+    assert.isFalse(checkbox.checked);
+    Promise.resolve().then(function() {
+      assert.isTrue(checkbox.checked);
+      checkbox.checked = false;
+      assert.isFalse(checkbox.checked);
+      return Promise.resolve().then(function() {
+        assert.isFalse(element.checked);
+        assert.isFalse(checkbox.checked);
+        checkbox.checked = true;
+        assert.isTrue(checkbox.checked);
+        return Promise.resolve().then(function() {
+          assert.isTrue(element.checked);
+          element.checked = true;
+          assert.isTrue(element.checked);
+          assert.isTrue(checkbox.checked);
+          element.checked = false;
+          assert.isFalse(element.checked);
+          assert.isTrue(checkbox.checked);
+          return Promise.resolve().then(function() {
+            assert.isFalse(checkbox.checked);
+            assert.isFalse(element.checked);
+            done();
+          });
+        });
+      });
+    }).catch(function(e) {
+      done(e);
+    });
+  });
+
   it("should connect template event handlers", function() {
     sandbox.appendChild(element);
     var inside = element.shadowRoot.getElementById("inside");
     inside.dispatchEvent(new CustomEvent("wrong-event"));
     assert.isNull(element.lastEvent);
     var event = new CustomEvent("test-event");
     inside.dispatchEvent(event);
     assert.equal(element.lastEvent, event);
   });
 
   it("should connect host event handlers", function() {
     sandbox.appendChild(element);
     element.dispatchEvent(new CustomEvent("wrong-event"));
     assert.isNull(element.lastEvent);
     var event = new CustomEvent("host-event");
     element.dispatchEvent(event);
     assert.equal(element.lastEvent, event);
   });
 
   it("should call shadowRootReady after creating the template instance", function() {
     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>
+</sky>