Generate all runtime files from dart.

test/codegen/expect/js/src/varargs.js

 dart_library.library('js/src/varargs', null, /* Imports */[
-  "dart/_runtime",
+  'dart/_runtime',
   'dart/core'
 ], /* Lazy imports */[
 ], function(exports, dart, core) {
   'use strict';
   let dartx = dart.dartx;
   class _Rest extends core.Object {
     _Rest() {
     }
   }
   dart.setSignature(_Rest, {
     constructors: () => ({_Rest: [_Rest, []]})
   });
   const rest = dart.const(new _Rest());
   function spread(args) {
     dart.throw(new core.StateError('The spread function cannot be called, ' + 'it should be compiled away.'));
   }
   dart.fn(spread);
   // Exports:
   exports.rest = rest;
   exports.spread = spread;
 });