Enable running of fasta tests on build bot.

pkg/testing/lib/src/zone_helper.dart

 // Copyright (c) 2016, 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.md file.
 
 /// Helper functions for running code in a Zone.
 library testing.zone_helper;
 
 import 'dart:async' show
     Completer,
     Future,
     ZoneSpecification,
     runZoned;
 
+import 'dart:io' show
+    exit,
+    stderr;
+
 import 'dart:isolate' show
     Capability,
     Isolate,
     ReceivePort;
 
 import 'log.dart' show
     logUncaughtError;
 
 Future runGuarded(
     Future f(),
     {void printLineOnStdout(line),
      void handleLateError(error, StackTrace stackTrace)}) {
 
   var printWrapper;
   if (printLineOnStdout != null) {
     printWrapper = (_1, _2, _3, String line) {
       printLineOnStdout(line);
     };
   }
 
   Completer completer = new Completer();
 
   handleUncaughtError(error, StackTrace stackTrace) {
     logUncaughtError(error, stackTrace);
     if (!completer.isCompleted) {
       completer.completeError(error, stackTrace);
     } else if (handleLateError != null) {
       handleLateError(error, stackTrace);
     } else {
-      // Delegate to parent.
-      throw error;
+      String errorString = "error.toString() failed.";
+      try {
+        errorString = "$error";
+      } catch (_) {
+        // Ignored.
+      }
+      stderr.write("$errorString\n" +
+          (stackTrace == null ? "" : "$stackTrace"));
+      stderr.flush();
+      exit(255);
     }
   }
 
   ZoneSpecification specification = new ZoneSpecification(print: printWrapper);
 
   ReceivePort errorPort = new ReceivePort();
   Future errorFuture = errorPort.listen((List errors) {
     Isolate.current.removeErrorListener(errorPort.sendPort);
     errorPort.close();
     var error = errors[0];
     var stackTrace = errors[1];
     if (stackTrace != null) {
       stackTrace = new StackTrace.fromString(stackTrace);
     }
     handleUncaughtError(error, stackTrace);
   }).asFuture();
 
+  Isolate.current.setErrorsFatal(false);
   Isolate.current.addErrorListener(errorPort.sendPort);
   return acknowledgeControlMessages(Isolate.current).then((_) {
     runZoned(
         () => new Future(f).then(completer.complete),
         zoneSpecification: specification,
         onError: handleUncaughtError);
 
     return completer.future.whenComplete(() {
       errorPort.close();
       Isolate.current.removeErrorListener(errorPort.sendPort);
       return acknowledgeControlMessages(Isolate.current)
           .then((_) => errorFuture);
     });
   });
 }
 
 /// Ping [isolate] to ensure control messages have been delivered.  Control
 /// messages are things like [Isolate.addErrorListener] and
 /// [Isolate.addOnExitListener].
 Future acknowledgeControlMessages(Isolate isolate, {Capability resume}) {
   ReceivePort ping = new ReceivePort();
   Isolate.current.ping(ping.sendPort);
   if (resume == null) {
     return ping.first;
   } else {
     return ping.first.then((_) => isolate.resume(resume));
   }
 }