Fix a crash.

lib/src/runner/reporter/compact.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.
 
 library test.runner.reporter.compact;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 
@@ skipping 192 matching lines @@
         error.innerError is! String) {
       print(indent(terseChain(stackTrace).toString()));
     }
   }
 
   /// A callback called when the engine is finished running tests.
   ///
   /// [success] will be `true` if all tests passed, `false` if some tests
   /// failed, and `null` if the engine was closed prematurely.
   void _onDone(bool success) {
-    _timer.cancel();
+    if (_timer != null) _timer.cancel();
     _timer = null;
     _stopwatch.stop();
 
     // A null success value indicates that the engine was closed before the
     // tests finished running, probably because of a signal from the user. We
     // shouldn't print summary information, we should just make sure the
     // terminal cursor is on its own line.
     if (success == null) {
       if (!_printedNewline) print("");
       _printedNewline = true;
@@ skipping 108 matching lines @@
 
     if (_printPlatform && liveTest.suite.platform != null) {
       name = "[${liveTest.suite.platform}] $name";
     }
 
     if (liveTest.suite is LoadSuite) name = "$_bold$_gray$name$_noColor";
 
     return name;
   }
 }