Check for duplicate library names

lib/runtime/dart/_isolate_helper.js

-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) {
     return new _Serializer().serialize(message);
   }
   dart.fn(_serializeMessage);
   function _deserializeMessage(message) {
     return new _Deserializer().deserialize(message);
   }
   dart.fn(_deserializeMessage);
@@ skipping 1536 matching lines @@
   exports.leaveJsAsync = leaveJsAsync;
   exports.isWorker = isWorker;
   exports.startRootIsolate = startRootIsolate;
   exports.IsolateNatives = IsolateNatives;
   exports.RawReceivePortImpl = RawReceivePortImpl;
   exports.ReceivePortImpl = ReceivePortImpl;
   exports.TimerImpl = TimerImpl;
   exports.hasTimer = hasTimer;
   exports.CapabilityImpl = CapabilityImpl;
 })(_isolate_helper, core, _native_typed_data, _interceptors, _js_helper, isolate, _foreign_helper, _js_embedded_names, collection, async);