Refactor runtime into libraries, better type reps

test/codegen/expect/8invalid-chars.in+file_name.js

-dart.library('8invalid-chars.in+file_name', null, /* Imports */[
+loader.library('8invalid-chars.in+file_name', null, /* Imports */[
+  "dart/dart_runtime",
+  "dart/dartx"
 ], /* Lazy imports */[
-], function(exports) {
+], function(exports, dart, dartx) {
   'use strict';
   function main() {
   }
   dart.fn(main);
   // Exports:
   exports.main = main;
 });