Add --modules=node support

test/codegen/expect/unittest.js

 dart_library.library('unittest', null, /* Imports */[
   'dart/_runtime',
   'matcher/matcher',
   'dom/dom',
   'dart/core',
   'dart/async',
   'matcher/src/interfaces',
   'matcher/src/util',
   'matcher/src/description'
 ], /* Lazy imports */[
-], function(exports, dart, matcher, dom, core, async, interfaces, util, description$) {
+], function(exports, dart, matcher, dom, core, $async, interfaces, util, description$) {
   'use strict';
   let dartx = dart.dartx;
-  dart.export(exports, matcher);
+  dart.export_(exports, matcher);
   function group(name, body) {
     return dart.dsend(dom.window, 'suite', name, body);
   }
   dart.fn(group, dart.void, [core.String, dart.functionType(dart.void, [])]);
   function test(name, body, opts) {
     let skip = opts && 'skip' in opts ? opts.skip : null;
     if (skip != null) {
       core.print(`SKIP ${name}: ${skip}`);
       return;
     }
     dart.dsend(dom.window, 'test', name, dart.fn(done => {
       function _finishTest(f) {
-        if (dart.is(f, async.Future)) {
+        if (dart.is(f, $async.Future)) {
           dart.dsend(f, 'then', _finishTest);
         } else {
           dart.dcall(done);
         }
       }
       dart.fn(_finishTest);
       _finishTest(body());
     }));
   }
   dart.fn(test, dart.void, [core.String, dart.functionType(dart.dynamic, [])], {skip: core.String});
@@ skipping 46 matching lines @@
   }
   dart.fn(_defaultFailFormatter, core.String, [dart.dynamic, interfaces.Matcher, core.String, core.Map, core.bool]);
   // Exports:
   exports.group = group;
   exports.test = test;
   exports.TestFailure = TestFailure;
   exports.ErrorFormatter = ErrorFormatter;
   exports.expect = expect;
   exports.fail = fail;
 });