fixes #52, fields shadowing getters/setters or other fields

lib/runtime/dart/isolate.js

 var isolate;
 (function(exports) {
   'use strict';
   class Capability extends core.Object {
     Capability() {
       return new _isolate_helper.CapabilityImpl();
     }
   }
   class IsolateSpawnException extends core.Object {
     IsolateSpawnException(message) {
-      this.message = message;
+      dart.initField(IsolateSpawnException, this, 'message', message);
     }
     toString() {
       return `IsolateSpawnException: ${this.message}`;
     }
   }
   IsolateSpawnException[dart.implements] = () => [core.Exception];
   let _currentIsolateCache = Symbol('_currentIsolateCache');
   let _pause = Symbol('_pause');
   class Isolate extends core.Object {
     Isolate(controlPort, opts) {
       let pauseCapability = opts && 'pauseCapability' in opts ? opts.pauseCapability : null;
       let terminateCapability = opts && 'terminateCapability' in opts ? opts.terminateCapability : null;
-      this.controlPort = controlPort;
-      this.pauseCapability = pauseCapability;
-      this.terminateCapability = terminateCapability;
+      dart.initField(Isolate, this, 'controlPort', controlPort);
+      dart.initField(Isolate, this, 'pauseCapability', pauseCapability);
+      dart.initField(Isolate, this, 'terminateCapability', terminateCapability);
     }
     static get current() {
       return Isolate[_currentIsolateCache];
     }
     static spawn(entryPoint, message, opts) {
       let paused = opts && 'paused' in opts ? opts.paused : false;
       try {
         return dart.as(_isolate_helper.IsolateNatives.spawnFunction(entryPoint, message, paused).then(dart.as(msg => new Isolate(dart.as(dart.dindex(msg, 1), SendPort), {pauseCapability: dart.as(dart.dindex(msg, 2), Capability), terminateCapability: dart.as(dart.dindex(msg, 3), Capability)}), dart.functionType(dart.dynamic, [core.List]))), async.Future$(Isolate));
       } catch (e) {
         let st = dart.stackTrace(e);
@@ skipping 148 matching lines @@
       this.stackTrace = stackTrace;
     }
     toString() {
       return 'IsolateUnhandledException: exception while handling message: ' + `${this.message} \n  ` + `${this.source.toString().replaceAll("\n", "\n  ")}\n` + 'original stack trace:\n  ' + `${this.stackTrace.toString().replaceAll("\n", "\n  ")}`;
     }
   }
   _IsolateUnhandledException[dart.implements] = () => [core.Exception];
   let _description = Symbol('_description');
   class RemoteError extends core.Object {
     RemoteError(description, stackDescription) {
-      this[_description] = description;
-      this.stackTrace = new _RemoteStackTrace(stackDescription);
+      dart.initField(RemoteError, this, _description, description);
+      dart.initField(RemoteError, this, 'stackTrace', new _RemoteStackTrace(stackDescription));
     }
     toString() {
       return this[_description];
     }
   }
   RemoteError[dart.implements] = () => [core.Error];
   let _trace = Symbol('_trace');
   class _RemoteStackTrace extends core.Object {
     _RemoteStackTrace(trace) {
       this[_trace] = trace;
     }
     toString() {
       return this[_trace];
     }
   }
   _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 = {}));