fixes #157, renaming local library identifiers if needed.

lib/runtime/dart/_js_names.js

Index: lib/runtime/dart/_js_names.js
diff --git a/lib/runtime/dart/_js_names.js b/lib/runtime/dart/_js_names.js
index 1c6f4a7b7811e0450e8329e314f22a8853a02da1..dbe83175cca265bec3233b1f70210ffcec57a2d9 100644
--- a/lib/runtime/dart/_js_names.js
+++ b/lib/runtime/dart/_js_names.js
@@ -1,5 +1,5 @@
-var _js_names;
-(function(exports) {
+var _js_names, _foreign_helper, _js_embedded_names, core, _interceptors, _js_helper;
+(function(exports, _foreign_helper, _js_embedded_names, core, _interceptors, _js_helper) {
   'use strict';
   // Function preserveNames: () → dynamic
   function preserveNames() {
@@ -76,4 +76,4 @@ var _js_names;
   exports.extractKeys = extractKeys;
   exports.unmangleGlobalNameIfPreservedAnyways = unmangleGlobalNameIfPreservedAnyways;
   exports.unmangleAllIdentifiersIfPreservedAnyways = unmangleAllIdentifiersIfPreservedAnyways;
-})(_js_names || (_js_names = {}));
+})(_js_names || (_js_names = {}), _foreign_helper || (_foreign_helper = {}), _js_embedded_names, core, _interceptors, _js_helper || (_js_helper = {}));