Check for duplicate library names

test/codegen/expect/sunflower/dom.js

Index: test/codegen/expect/sunflower/dom.js
diff --git a/test/codegen/expect/sunflower/dom.js b/test/codegen/expect/sunflower/dom.js
index 48461cb9f55575589f4dd91f510461118b084af3..d999a8fedebfdd1f1d87da48f67dd4b1e8388c14 100644
--- a/test/codegen/expect/sunflower/dom.js
+++ b/test/codegen/expect/sunflower/dom.js
@@ -1,6 +1,7 @@
-var dom = dart.defineLibrary(dom, window);
-var core = dart.import(core);
-(function(exports, core) {
+dart.library('dom.js', window, /* Imports */[
+  'dart/core.js'
+], /* Lazy imports */[
+], function(exports, core) {
   'use strict';
   class JsName extends core.Object {
     JsName(opts) {
@@ -48,4 +49,4 @@ var core = dart.import(core);
   exports.RenderingContext = RenderingContext;
   exports.CanvasDrawingStyles = CanvasDrawingStyles;
   exports.CanvasPathMethods = CanvasPathMethods;
-})(dom, core);
+});