fixes #157, renaming local library identifiers if needed.

test/codegen/expect/sunflower/sunflower.js

Index: test/codegen/expect/sunflower/sunflower.js
diff --git a/test/codegen/expect/sunflower/sunflower.js b/test/codegen/expect/sunflower/sunflower.js
index 6a14e4c576984ee58158b5d649b23073f21cbec2..15772ba3899eb3751b25e8ef44ee79ef3b8f5312 100644
--- a/test/codegen/expect/sunflower/sunflower.js
+++ b/test/codegen/expect/sunflower/sunflower.js
@@ -1,5 +1,8 @@
-var sunflower;
-(function(exports) {
+var sunflower = dart.defineLibrary(sunflower, {});
+var math = dart.import(math);
+var dom = dart.import(dom);
+var core = dart.import(core);
+(function(exports, math, dom, core) {
   'use strict';
   let ORANGE = "orange";
   let SEED_RADIUS = 2;
@@ -91,4 +94,4 @@ var sunflower;
   exports.SunflowerSeed = SunflowerSeed;
   exports.Circle = Circle;
   exports.CirclePainter = CirclePainter;
-})(sunflower || (sunflower = {}));
+})(sunflower, math, dom, core);