fixes #69, avoid module name inside module scope

test/codegen/expect/BenchmarkBase/BenchmarkBase.js

 var BenchmarkBase;
-(function(BenchmarkBase) {
+(function(exports) {
   'use strict';
   class Expect extends dart.Object {
     static equals(expected, actual) {
       if (!dart.equals(expected, actual)) {
         throw `Values not equal: ${expected} vs ${actual}`;
       }
     }
     static listEquals(expected, actual) {
       if (expected.length !== actual.length) {
         throw `Lists have different lengths: ${expected.length} vs ${actual.length}`;
@@ skipping 44 matching lines @@
       }).bind(this), 2000);
       this.teardown();
       return result;
     }
     report() {
       let score = this.measure();
       core.print(`${this.name}(RunTime): ${score} us.`);
     }
   }
   // Exports:
-  BenchmarkBase.Expect = Expect;
-  BenchmarkBase.BenchmarkBase = BenchmarkBase;
+  exports.Expect = Expect;
+  exports.BenchmarkBase = BenchmarkBase;
 })(BenchmarkBase || (BenchmarkBase = {}));