Refactor runtime into libraries, better type reps

lib/runtime/dart/core.js

Index: lib/runtime/dart/core.js
diff --git a/lib/runtime/dart/core.js b/lib/runtime/dart/core.js
index baee9708176073cd53205e6aa6a062c92983da0e..8ff97330c997f6ef24265262578e619aa69d854e 100644
--- a/lib/runtime/dart/core.js
+++ b/lib/runtime/dart/core.js
@@ -1,12 +1,14 @@
-dart.library('dart/core', null, /* Imports */[
+dart_library.library('dart/core', null, /* Imports */[
+  "dart_runtime/dart"
 ], /* Lazy imports */[
   'dart/_js_helper',
   'dart/_internal',
   'dart/collection',
   'dart/_interceptors',
   'dart/convert'
-], function(exports, _js_helper, _internal, collection, _interceptors, convert) {
+], function(exports, dart, _js_helper, _internal, collection, _interceptors, convert) {
   'use strict';
+  let dartx = dart.dartx;
   class Object {
     constructor() {
       let name = this.constructor.name;