Get rid of Chain.track in pub.

sdk/lib/_internal/pub/test/test_pub.dart

 // Copyright (c) 2013, 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.
 library test_pub;
@@ skipping 916 matching lines @@
 
 /// Schedules a single [Validator] to run on the [appPath].
 ///
 /// Returns a scheduled Future that contains the errors and warnings produced
 /// by that validator.
 Future<Pair<List<String>, List<String>>> schedulePackageValidation(
     ValidatorCreator fn) {
   return schedule(() {
     var cache = new SystemCache.withSources(p.join(sandboxDir, cachePath));
 
-    return syncFuture(() {
+    return new Future.sync(() {
       var validator = fn(new Entrypoint(p.join(sandboxDir, appPath), cache));
       return validator.validate().then((_) {
         return new Pair(validator.errors, validator.warnings);
       });
     });
   }, "validating package");
 }
 
 /// A matcher that matches a Pair.
 Matcher pairOf(Matcher firstMatcher, Matcher lastMatcher) =>
@@ skipping 11 matching lines @@
         _lastMatcher.matches(item.last, matchState);
   }
 
   Description describe(Description description) {
     return description.addAll("(", ", ", ")", [_firstMatcher, _lastMatcher]);
   }
 }
 
 /// A [StreamMatcher] that matches multiple lines of output.
 StreamMatcher emitsLines(String output) => inOrder(output.split("\n"));