pkg/test: cleanup imports

lib/src/runner/vm/catch_isolate_errors.dart

 // Copyright (c) 2015, 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.
 
+import 'dart:async';
 import 'dart:isolate';
-import 'dart:async';
 
 import 'package:stack_trace/stack_trace.dart';
 
 /// Capture any top-level errors (mostly lazy syntax errors, since other are
 /// caught below) and report them to the parent isolate.
 void catchIsolateErrors() {
   var errorPort = new ReceivePort();
   // Aet errors non-fatal because otherwise they'll be double-printed.
   Isolate.current.setErrorsFatal(false);
   Isolate.current.addErrorListener(errorPort.sendPort);
   errorPort.listen((message) {
     // Masquerade as an IsoalteSpawnException because that's what this would
     // be if the error had been detected statically.
     var error = new IsolateSpawnException(message[0]);
     var stackTrace =
         message[1] == null ? new Trace([]) : new Trace.parse(message[1]);
     Zone.current.handleUncaughtError(error, stackTrace);
   });
 }