Change Process.start to return a future that completes with a

tools/testing/dart/co19_test.dart

 // 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.
 
 /**
  * Tool for running co19 tests. Used when updating co19.
  *
  * Currently, this tool is merely a convenience around multiple
  * invocations of test.dart. Long term, we hope to evolve this into a
  * script that can automate most of the tasks necessary when updating
@@ skipping 41 matching lines @@
   }
   if (configurations == null || configurations.isEmpty()) return;
 
   var firstConfiguration = configurations[0];
   Map<String, RegExp> selectors = firstConfiguration['selectors'];
   var maxProcesses = firstConfiguration['tasks'];
   var verbose = firstConfiguration['verbose'];
   var listTests = firstConfiguration['list'];
 
   var configurationIterator = configurations.iterator();
-  bool enqueueConfiguration(ProcessQueue queue) {
-    if (!configurationIterator.hasNext()) {
-      return false;
-    }
-
+  void enqueueConfiguration(ProcessQueue queue) {
+    if (!configurationIterator.hasNext()) return;
     var configuration = configurationIterator.next();
     for (String selector in selectors.getKeys()) {
       if (selector == 'co19') {
         queue.addTestSuite(new Co19TestSuite(configuration));
       } else {
         throw 'Error: unexpected selector: "$selector".';
       }
     }
-    return true;
   }
 
   // Start process queue.
   var queue = new ProcessQueue(maxProcesses,
                                'diff',
                                startTime,
                                false,
                                enqueueConfiguration,
                                () {},
                                verbose,
                                listTests);
 }