Specs: fix typos in style2.md, checkin forgotten builtins.md, add guard feature to runloop.md, rena…

sky/specs/events.md

 Sky Event Model
 ===============
 
 ```dart
 import 'dart:collection';
 import 'dart:async';
 
 class ExceptionAndStackTrace<T> {
   const ExceptionAndStackTrace(this.exception, this.stackTrace);
   final T exception;
@@ skipping 13 matching lines @@
 
 typedef bool Filter<T>(T t);
 typedef void Handler<T>(T t);
 
 class DispatcherController<T> {
   DispatcherController() : dispatcher = new Dispatcher<T>();
   final Dispatcher<T> dispatcher;
   void add(T data) => dispatcher._add(data);
 }
 
-class Pair<A, B> {
-  const Pair(this.a, this.b);
-  final A a;
-  final B b;
-}
-
 class Dispatcher<T> {
   List<Pair<Handler, ZoneUnaryCallback>> _listeners;
   void listen(Handler<T> handler) {
     // you should not throw out of this handler
     if (_listeners == null)
       _listeners = new List<Pair<Handler, ZoneUnaryCallback>>();
     _listeners.add(new Pair<Handler, ZoneUnaryCallback>(handler, Zone.current.bindUnaryCallback(handler)));
   }
   bool unlisten(Handler<T> handler) {
     if (_listeners == null)
@@ skipping 139 matching lines @@
       throw exceptions;
     return event.result;
   }
 
   void _dispatchEventLocally(Event event) {
     event._currentTarget = this;
     _eventsController.add(event);
   }
 }
 ```