Refactor runtime into libraries, better type reps

test/codegen/expect/cascade.js

Index: test/codegen/expect/cascade.js
diff --git a/test/codegen/expect/cascade.js b/test/codegen/expect/cascade.js
index 0a273d9eb6c8b1fe39b7e909443e0c21326f66af..7791c0824ad3858dadca42c5eccec0c3f909bfcf 100644
--- a/test/codegen/expect/cascade.js
+++ b/test/codegen/expect/cascade.js
@@ -1,8 +1,10 @@
-dart.library('cascade', null, /* Imports */[
+dart_library.library('cascade', null, /* Imports */[
+  "dart_runtime/dart",
   'dart/core'
 ], /* Lazy imports */[
-], function(exports, core) {
+], function(exports, dart, core) {
   'use strict';
+  let dartx = dart.dartx;
   class A extends core.Object {
     A() {
       this.x = null;