fixes #157, renaming local library identifiers if needed.

lib/runtime/dart/math.js

Index: lib/runtime/dart/math.js
diff --git a/lib/runtime/dart/math.js b/lib/runtime/dart/math.js
index 16abfaec7497520753be012e76dc80c88c9414a1..ec2ad3bd855f27c4bbbde981f532d9ab2e7a55ea 100644
--- a/lib/runtime/dart/math.js
+++ b/lib/runtime/dart/math.js
@@ -1,5 +1,5 @@
-var math;
-(function(exports) {
+var math, core, _js_helper;
+(function(exports, core, _js_helper) {
   'use strict';
   class _JenkinsSmiHash extends core.Object {
     static combine(hash, value) {
@@ -460,4 +460,4 @@ var math;
   exports.sqrt = sqrt;
   exports.exp = exp;
   exports.log = log;
-})(math || (math = {}));
+})(math || (math = {}), core, _js_helper || (_js_helper = {}));