Check for duplicate library names

test/codegen/expect/dir/html_input_a.js

Index: test/codegen/expect/dir/html_input_a.js
diff --git a/test/codegen/expect/dir/html_input_a.js b/test/codegen/expect/dir/html_input_a.js
index d2c8d70f17d895298e93674e116cf23a548f805f..e70ca0963fc035f31d7bd8981efd178cb1ea6c0d 100644
--- a/test/codegen/expect/dir/html_input_a.js
+++ b/test/codegen/expect/dir/html_input_a.js
@@ -1,9 +1,10 @@
-var html_input_a = dart.defineLibrary(html_input_a, {});
-var core = dart.import(core);
-var html_input_b = dart.import(html_input_b);
-var html_input_c = dart.import(html_input_c);
-var html_input_d = dart.import(html_input_d);
-(function(exports, core, html_input_b, html_input_c, html_input_d) {
+dart.library('dir/html_input_a.js', null, /* Imports */[
+  'dart/core.js',
+  'dir/html_input_b.js',
+  'dir/html_input_c.js',
+  'dir/html_input_d.js'
+], /* Lazy imports */[
+], function(exports, core, html_input_b, html_input_c, html_input_d) {
   'use strict';
   function main() {
     core.print(`fib(${html_input_b.x} + ${html_input_c.y}) = `);
@@ -12,4 +13,4 @@ var html_input_d = dart.import(html_input_d);
   dart.fn(main);
   // Exports:
   exports.main = main;
-})(html_input_a, core, html_input_b, html_input_c, html_input_d);
+});