Change dart:io to use Future for one-shot operations.

utils/tests/pub/test_pub.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.
 
 /**
  * Test infrastructure for testing pub. Unlike typical unit tests, most pub
  * tests are integration tests that stage some stuff on the file system, run
  * pub, and then validate the results. This library provides an API to build
  * tests like that.
  */
@@ skipping 119 matching lines @@
   if (sdk == null) return new Future.immediate(null);
 
   return dir('sdk', sdk).create(sandboxDir);
 }
 
 Future<ProcessResult> _runPub(List<String> pubArgs, String workingDir) {
   // Find a dart executable we can use to run pub. Uses the one that the
   // test infrastructure uses.
   final scriptDir = new File(new Options().script).directorySync().path;
   final platform = Platform.operatingSystem;
-  final dartBin = join(scriptDir, '../../../tools/testing/bin/$platform/dart');
+  final dartBin = new File(new Options().executable).fullPathSync();
 
   // Find the main pub entrypoint.
   final pubPath = fs.joinPaths(scriptDir, '../../pub/pub.dart');
 
   final args = ['--enable-type-checks', '--enable-asserts', pubPath];
   args.addAll(pubArgs);
 
   return runProcess(dartBin, args, workingDir);
 }
 
@@ skipping 173 matching lines @@
     return Futures.wait(entryFutures).transform((entries) {
       for (final entry in entries) {
         if (entry != null) return entry;
       }
 
       // If we got here, all of the sub-entries were valid.
       return null;
     });
   }
 }