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..7b93333fc435148e14991c7f762945e06e8d63d3 100644
--- a/lib/runtime/dart/math.js
+++ b/lib/runtime/dart/math.js
@@ -1,5 +1,7 @@
-var math;
-(function(exports) {
+var math = dart.defineLibrary(math, {});
+var core = dart.import(core);
+var _js_helper = dart.lazyImport(_js_helper);
+(function(exports, core, _js_helper) {
   'use strict';
   class _JenkinsSmiHash extends core.Object {
     static combine(hash, value) {
@@ -460,4 +462,4 @@ var math;
   exports.sqrt = sqrt;
   exports.exp = exp;
   exports.log = log;
-})(math || (math = {}));
+})(math, core, _js_helper);