Added TodoMVC startup benchmarks.

samples/third_party/todomvc_performance/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) {
       e.preventDefault();
       fire('td-input-commit');
     }
   }
 
   keyupAction(e) {
     if (e.keyCode == KeyCode.ESC) {
       fire('td-input-cancel');
     }
   }
 }