Refactor runtime into libraries, better type reps

test/codegen/expect/temps.js

-dart.library('temps', null, /* Imports */[
+dart_library.library('temps', null, /* Imports */[
+  "dart_runtime/dart",
   'dart/core'
 ], /* Lazy imports */[
-], function(exports, core) {
+], function(exports, dart, core) {
   'use strict';
+  let dartx = dart.dartx;
   let _x = Symbol('_x');
   let __x = Symbol('__x');
   let _function = Symbol('_function');
   class FormalCollision extends core.Object {
     FormalCollision(x, _x$, func) {
       this[_x] = x;
       this[__x] = _x$;
       this[_function] = func;
     }
   }
@@ skipping 23 matching lines @@
     core.print(new FormalCollision(1, 2, dart.fn(x => x)));
     core.print(new OptionalArg()[_opt]);
     core.print(new OptionalArg.named()[_opt]);
   }
   dart.fn(main);
   // Exports:
   exports.FormalCollision = FormalCollision;
   exports.OptionalArg = OptionalArg;
   exports.main = main;
 });