Check for duplicate library names

lib/runtime/dart/_isolate_helper.js

Index: lib/runtime/dart/_isolate_helper.js
diff --git a/lib/runtime/dart/_isolate_helper.js b/lib/runtime/dart/_isolate_helper.js
index 14722e3181c4603cb15f0fe68a5e018dec8ac9cb..5140d86a5cf571986a5fda25e3beb1c3549df8ee 100644
--- a/lib/runtime/dart/_isolate_helper.js
+++ b/lib/runtime/dart/_isolate_helper.js
@@ -1,13 +1,13 @@
-var _isolate_helper = dart.defineLibrary(_isolate_helper, {});
-var core = dart.import(core);
-var _native_typed_data = dart.import(_native_typed_data);
-var _interceptors = dart.lazyImport(_interceptors);
-var _js_helper = dart.lazyImport(_js_helper);
-var isolate = dart.import(isolate);
-var _foreign_helper = dart.import(_foreign_helper);
-var _js_embedded_names = dart.import(_js_embedded_names);
-var collection = dart.import(collection);
-var async = dart.import(async);
+dart.defineLibrary('_isolate_helper');
+dart.import('core');
+dart.import('_native_typed_data');
+dart.lazyImport('_interceptors');
+dart.lazyImport('_js_helper');
+dart.import('isolate');
+dart.import('_foreign_helper');
+dart.import('_js_embedded_names');
+dart.import('collection');
+dart.import('async');
 (function(exports, core, _native_typed_data, _interceptors, _js_helper, isolate, _foreign_helper, _js_embedded_names, collection, async) {
   'use strict';
   function _serializeMessage(message) {