Update TodoMVC based on https://github.com/polymer/todomvc

samples/third_party/todomvc/web/elements/td_input.dart

+library todomvc.web.elements.td_input;
+
+import 'dart:html';
+import 'package:polymer/polymer.dart';
+
+@CustomTag('td-input')
+class TodoInput extends InputElement with Polymer, Observable {
+  factory TodoInput() => new Element.tag('input', 'td-input');
+  TodoInput.created() : super.created() { polymerCreated(); }
+
+  keypressAction(e) {
+    // Listen for enter on keypress but esc on keyup, because
+    // IE doesn't fire keyup for enter.
+    if (e.keyCode == KeyCode.ENTER) {
+      fire('td-input-commit');
+    }
+  }
+
+  keyupAction(e) {
+    if (e.keyCode == KeyCode.ESC) {
+      fire('td-input-cancel');
+    }
+  }
+}