Check for duplicate library names

test/codegen/expect/cascade.js

Index: test/codegen/expect/cascade.js
diff --git a/test/codegen/expect/cascade.js b/test/codegen/expect/cascade.js
index a5f8babda0f22294bb08b3790e13ee66d8086fb0..ab5728a7916a6a5adfc4e0fff01f15daeb6c1c2d 100644
--- a/test/codegen/expect/cascade.js
+++ b/test/codegen/expect/cascade.js
@@ -1,6 +1,7 @@
-var cascade = dart.defineLibrary(cascade, {});
-var core = dart.import(core);
-(function(exports, core) {
+dart.library('cascade', null, /* Imports */[
+  'dart/core'
+], /* Lazy imports */[
+], function(exports, core) {
   'use strict';
   class A extends core.Object {
     A() {
@@ -119,4 +120,4 @@ var core = dart.import(core);
   exports.Base$ = Base$;
   exports.Base = Base;
   exports.Foo = Foo;
-})(cascade, core);
+});