Check for duplicate library names

lib/runtime/dart/async.js

-var async = dart.defineLibrary(async, {});
-var core = dart.import(core);
-var _internal = dart.import(_internal);
-var _js_helper = dart.lazyImport(_js_helper);
-var _isolate_helper = dart.lazyImport(_isolate_helper);
-var collection = dart.import(collection);
-(function(exports, core, _internal, _js_helper, _isolate_helper, collection) {
+dart.library('dart/async.js', null, /* Imports */[
+  'dart/core.js',
+  'dart/_internal.js',
+  'dart/collection.js'
+], /* Lazy imports */[
+  'dart/_js_helper.js',
+  'dart/_isolate_helper.js'
+], function(exports, core, _internal, collection, _js_helper, _isolate_helper) {
   'use strict';
   function _invokeErrorHandler(errorHandler, error, stackTrace) {
     if (dart.is(errorHandler, ZoneBinaryCallback)) {
       return dart.dcall(errorHandler, error, stackTrace);
     } else {
       return dart.dcall(errorHandler, error);
     }
   }
   dart.fn(_invokeErrorHandler, core.Object, [core.Function, core.Object, core.StackTrace]);
   function _registerErrorHandler(errorHandler, zone) {
@@ skipping 5882 matching lines @@
   exports.ErrorCallbackHandler = ErrorCallbackHandler;
   exports.ScheduleMicrotaskHandler = ScheduleMicrotaskHandler;
   exports.CreateTimerHandler = CreateTimerHandler;
   exports.CreatePeriodicTimerHandler = CreatePeriodicTimerHandler;
   exports.PrintHandler = PrintHandler;
   exports.ForkHandler = ForkHandler;
   exports.ZoneSpecification = ZoneSpecification;
   exports.ZoneDelegate = ZoneDelegate;
   exports.Zone = Zone;
   exports.runZoned = runZoned;
-})(async, core, _internal, _js_helper, _isolate_helper, collection);
+});