fix bug in isolate code, reenable isolate tests

lib/isolate/frog/natives.js

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Top-level native code needed by the frog compiler
 
 var $globalThis = this;
 var $globals = null;
 var $globalState = null;
 function $initGlobals(context) { context.isolateStatics = {}; }
 function $setGlobals(context) { $globals = context.isolateStatics; }
 
 // Wrap a 0-arg dom-callback to bind it with the current isolate:
 function $wrap_call$0(fn) { return fn && fn.wrap$call$0(); }
 
 Function.prototype.wrap$call$0 = function() {
   var isolateContext = $globalState.currentContext;
   var self = this;
   this.wrap$0 = function() {
-    isolateContext.eval(self);
+    var res = isolateContext.eval(self);
     $globalState.topEventLoop.run();
+    return res;
   };
   this.wrap$call$0 = function() { return this.wrap$0; };
   return this.wrap$0;
 };
 
 // Wrap a 1-arg dom-callback to bind it with the current isolate:
 function $wrap_call$1(fn) { return fn && fn.wrap$call$1(); }
 
 Function.prototype.wrap$call$1 = function() {
   var isolateContext = $globalState.currentContext;
   var self = this;
   this.wrap$1 = function(arg) {
-    isolateContext.eval(function() { self(arg); });
+    var res = isolateContext.eval(function() { return self(arg); });
     $globalState.topEventLoop.run();
+    return res;
   };
   this.wrap$call$1 = function() { return this.wrap$1; };
   return this.wrap$1;
 };