Refactor runtime into libraries, better type reps

lib/runtime/dart/async.js

-dart.library('dart/async', null, /* Imports */[
+dart_library.library('dart/async', null, /* Imports */[
+  "dart_runtime/dart",
   'dart/core',
   'dart/_internal',
   'dart/collection'
 ], /* Lazy imports */[
   'dart/_isolate_helper',
   'dart/_js_helper'
-], function(exports, core, _internal, collection, _isolate_helper, _js_helper) {
+], function(exports, dart, core, _internal, collection, _isolate_helper, _js_helper) {
   'use strict';
+  let dartx = dart.dartx;
   function _invokeErrorHandler(errorHandler, error, stackTrace) {
     if (dart.is(errorHandler, ZoneBinaryCallback)) {
       return dart.dcall(errorHandler, error, stackTrace);
     } else {
       return dart.dcall(errorHandler, error);
     }
   }
   dart.fn(_invokeErrorHandler, core.Object, [core.Function, core.Object, core.StackTrace]);
   function _registerErrorHandler(errorHandler, zone) {
     if (dart.is(errorHandler, ZoneBinaryCallback)) {
@@ skipping 5882 matching lines @@
   exports.ScheduleMicrotaskHandler = ScheduleMicrotaskHandler;
   exports.CreateTimerHandler = CreateTimerHandler;
   exports.CreatePeriodicTimerHandler = CreatePeriodicTimerHandler;
   exports.PrintHandler = PrintHandler;
   exports.ForkHandler = ForkHandler;
   exports.ZoneSpecification = ZoneSpecification;
   exports.ZoneDelegate = ZoneDelegate;
   exports.Zone = Zone;
   exports.runZoned = runZoned;
 });