fixes #157, renaming local library identifiers if needed.

lib/runtime/dart/isolate.js

-var isolate;
-(function(exports) {
+var isolate, core, _isolate_helper, async;
+(function(exports, core, _isolate_helper, async) {
   'use strict';
   class Capability extends core.Object {
     Capability() {
       return new _isolate_helper.CapabilityImpl();
     }
   }
   class IsolateSpawnException extends core.Object {
     IsolateSpawnException(message) {
       this.message = message;
     }
@@ skipping 197 matching lines @@
   }
   _RemoteStackTrace[dart.implements] = () => [core.StackTrace];
   // Exports:
   exports.Capability = Capability;
   exports.IsolateSpawnException = IsolateSpawnException;
   exports.Isolate = Isolate;
   exports.SendPort = SendPort;
   exports.ReceivePort = ReceivePort;
   exports.RawReceivePort = RawReceivePort;
   exports.RemoteError = RemoteError;
-})(isolate || (isolate = {}));
+})(isolate || (isolate = {}), core, _isolate_helper || (_isolate_helper = {}), async);