Check for duplicate library names

lib/runtime/dart/_internal.js

Index: lib/runtime/dart/_internal.js
diff --git a/lib/runtime/dart/_internal.js b/lib/runtime/dart/_internal.js
index e1ddf9fd76a0dab1ebbab28314e625a786087424..c2d685a35d4c88075b024eda1e808b35b6c0f177 100644
--- a/lib/runtime/dart/_internal.js
+++ b/lib/runtime/dart/_internal.js
@@ -1,10 +1,11 @@
-var _internal = dart.defineLibrary(_internal, {});
-var core = dart.import(core);
-var collection = dart.import(collection);
-var math = dart.lazyImport(math);
-var _interceptors = dart.lazyImport(_interceptors);
-var _js_primitives = dart.lazyImport(_js_primitives);
-(function(exports, core, collection, math, _interceptors, _js_primitives) {
+dart.library('dart/_internal', null, /* Imports */[
+  'dart/core',
+  'dart/collection'
+], /* Lazy imports */[
+  'dart/math',
+  'dart/_interceptors',
+  'dart/_js_primitives'
+], function(exports, core, collection, math, _interceptors, _js_primitives) {
   'use strict';
   class EfficientLength extends core.Object {}
   let ListIterable$ = dart.generic(function(E) {
@@ -2427,4 +2428,4 @@ var _js_primitives = dart.lazyImport(_js_primitives);
   exports.Sort = Sort;
   exports.Symbol = Symbol;
   exports.POWERS_OF_TEN = POWERS_OF_TEN;
-})(_internal, core, collection, math, _interceptors, _js_primitives);
+});