fixes #157, renaming local library identifiers if needed.

test/codegen/expect/BenchmarkBase.js

Index: test/codegen/expect/BenchmarkBase.js
diff --git a/test/codegen/expect/BenchmarkBase.js b/test/codegen/expect/BenchmarkBase.js
index 33c7b2e6adeafe8a746344a62138b165cd38cdce..96e2fe3217fee7a91de5ace6c51c3a808a7649bb 100644
--- a/test/codegen/expect/BenchmarkBase.js
+++ b/test/codegen/expect/BenchmarkBase.js
@@ -1,5 +1,6 @@
-var BenchmarkBase;
-(function(exports) {
+var BenchmarkBase = dart.defineLibrary(BenchmarkBase, {});
+var core = dart.import(core);
+(function(exports, core) {
   'use strict';
   class Expect extends core.Object {
     static equals(expected, actual) {
@@ -66,4 +67,4 @@ var BenchmarkBase;
   // Exports:
   exports.Expect = Expect;
   exports.BenchmarkBase = BenchmarkBase;
-})(BenchmarkBase || (BenchmarkBase = {}));
+})(BenchmarkBase, core);