Check for duplicate library names

lib/runtime/dart/_js_helper.js

Index: lib/runtime/dart/_js_helper.js
diff --git a/lib/runtime/dart/_js_helper.js b/lib/runtime/dart/_js_helper.js
index abd9a93d6e7dd93ee4e07bc832d010bb5158b2e2..43d9a7c7faa6e15919133750cc4f1a9bd2c551d2 100644
--- a/lib/runtime/dart/_js_helper.js
+++ b/lib/runtime/dart/_js_helper.js
@@ -1,13 +1,13 @@
-var _js_helper = dart.defineLibrary(_js_helper, {});
-var core = dart.import(core);
-var collection = dart.import(collection);
-var _internal = dart.import(_internal);
-var _foreign_helper = dart.import(_foreign_helper);
-var _js_embedded_names = dart.import(_js_embedded_names);
-var _interceptors = dart.lazyImport(_interceptors);
-var _js_names = dart.import(_js_names);
-var async = dart.import(async);
-var _isolate_helper = dart.lazyImport(_isolate_helper);
+dart.defineLibrary('_js_helper');
+dart.import('core');
+dart.import('collection');
+dart.import('_internal');
+dart.import('_foreign_helper');
+dart.import('_js_embedded_names');
+dart.lazyImport('_interceptors');
+dart.import('_js_names');
+dart.import('async');
+dart.lazyImport('_isolate_helper');
 (function(exports, core, collection, _internal, _foreign_helper, _js_embedded_names, _interceptors, _js_names, async, _isolate_helper) {
   'use strict';
   class NoSideEffects extends core.Object {