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);
-(function(exports, core, _native_typed_data, _interceptors, _js_helper, isolate, _foreign_helper, _js_embedded_names, collection, async) {
+dart.library('dart/_isolate_helper.js', null, /* Imports */[
+  'dart/core.js',
+  'dart/_native_typed_data.js',
+  'dart/isolate.js',
+  'dart/_foreign_helper.js',
+  'dart/_js_embedded_names.js',
+  'dart/collection.js',
+  'dart/async.js'
+], /* Lazy imports */[
+  'dart/_interceptors.js',
+  'dart/_js_helper.js'
+], function(exports, core, _native_typed_data, isolate, _foreign_helper, _js_embedded_names, collection, async, _interceptors, _js_helper) {
   'use strict';
   function _serializeMessage(message) {
     return new _Serializer().serialize(message);
   }
   dart.fn(_serializeMessage);
   function _deserializeMessage(message) {
     return new _Deserializer().deserialize(message);
   }
   dart.fn(_deserializeMessage);
   function _clone(message) {
@@ skipping 1534 matching lines @@
   exports.enterJsAsync = enterJsAsync;
   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);
+});