Check for duplicate library names

test/codegen/expect/opassign.js

Index: test/codegen/expect/opassign.js
diff --git a/test/codegen/expect/opassign.js b/test/codegen/expect/opassign.js
index 3429d82797983c17f7fb8df6a84c648e40a7989a..2710e69907d19df2c7ceb612ce175d07f4d8ec30 100644
--- a/test/codegen/expect/opassign.js
+++ b/test/codegen/expect/opassign.js
@@ -1,6 +1,7 @@
-var opassign = dart.defineLibrary(opassign, {});
-var core = dart.import(core);
-(function(exports, core) {
+dart.library('opassign', null, /* Imports */[
+  'dart/core'
+], /* Lazy imports */[
+], function(exports, core) {
   'use strict';
   dart.copyProperties(exports, {
     get index() {
@@ -54,4 +55,4 @@ var core = dart.import(core);
   exports.Foo = Foo;
   exports.main = main;
   exports.forcePostfix = forcePostfix;
-})(opassign, core);
+});