Refactor runtime into libraries, better type reps

lib/runtime/dart/_isolate_helper.js

-dart.library('dart/_isolate_helper', null, /* Imports */[
+dart_library.library('dart/_isolate_helper', null, /* Imports */[
+  "dart_runtime/dart",
   'dart/core',
   'dart/_interceptors',
   'dart/_js_helper',
   'dart/isolate',
   'dart/_foreign_helper',
   'dart/collection',
   'dart/async'
 ], /* Lazy imports */[
   'dart/_native_typed_data',
   'dart/_js_embedded_names'
-], function(exports, core, _interceptors, _js_helper, isolate, _foreign_helper, collection, async, _native_typed_data, _js_embedded_names) {
+], function(exports, dart, core, _interceptors, _js_helper, isolate, _foreign_helper, collection, async, _native_typed_data, _js_embedded_names) {
   'use strict';
+  let dartx = dart.dartx;
   function _serializeMessage(message) {
     return new _Serializer().serialize(message);
   }
   dart.fn(_serializeMessage);
   function _deserializeMessage(message) {
     return new _Deserializer().deserialize(message);
   }
   dart.fn(_deserializeMessage);
   function _clone(message) {
     let serializer = new _Serializer({serializeSendPorts: false});
@@ skipping 1528 matching lines @@
   exports.leaveJsAsync = leaveJsAsync;
   exports.isWorker = isWorker;
   exports.startRootIsolate = startRootIsolate;
   exports.IsolateNatives = IsolateNatives;
   exports.RawReceivePortImpl = RawReceivePortImpl;
   exports.ReceivePortImpl = ReceivePortImpl;
   exports.TimerImpl = TimerImpl;
   exports.hasTimer = hasTimer;
   exports.CapabilityImpl = CapabilityImpl;
 });