Refactor runtime into libraries, better type reps

test/codegen/expect/BenchmarkBase.js

-dart.library('BenchmarkBase', null, /* Imports */[
+dart_library.library('BenchmarkBase', null, /* Imports */[
+  "dart_runtime/dart",
   'dart/core'
 ], /* Lazy imports */[
-], function(exports, core) {
+], function(exports, dart, core) {
   'use strict';
+  let dartx = dart.dartx;
   class Expect extends core.Object {
     static equals(expected, actual) {
       if (!dart.equals(expected, actual)) {
         throw `Values not equal: ${expected} vs ${actual}`;
       }
     }
     static listEquals(expected, actual) {
       if (expected[dartx.length] != actual[dartx.length]) {
         throw `Lists have different lengths: ${expected[dartx.length]} vs ${actual[dartx.length]}`;
       }
@@ skipping 68 matching lines @@
       measure: [core.double, []],
       report: [dart.void, []]
     }),
     statics: () => ({measureFor: [core.double, [core.Function, core.int]]}),
     names: ['measureFor']
   });
   // Exports:
   exports.Expect = Expect;
   exports.BenchmarkBase = BenchmarkBase;
 });