Get rid of Chain.track in pub.

sdk/lib/_internal/pub/lib/src/global_packages.dart

 // Copyright (c) 2014, 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 pub.global_packages;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
@@ skipping 267 matching lines @@
 
     return true;
   }
 
   /// Finds the active package with [name].
   ///
   /// Returns an [Entrypoint] loaded with the active package if found.
   Future<Entrypoint> find(String name) {
     // TODO(rnystrom): Use async/await here when on __ catch is supported.
     // See: https://github.com/dart-lang/async_await/issues/27
-    return syncFuture(() {
+    return new Future.sync(() {
       var lockFilePath = _getLockFilePath(name);
       var lockFile;
       try {
         lockFile = new LockFile.load(lockFilePath, cache.sources);
       } on IOException catch (error) {
         var oldLockFilePath = p.join(_directory, '$name.lock');
         try {
           // TODO(nweiz): This looks for Dart 1.6's old lockfile location.
           // Remove it when Dart 1.6 is old enough that we don't think anyone
           // will have these lockfiles anymore (issue 20703).
@@ skipping 289 matching lines @@
         continue;
       }
 
       if (match[1] == package) {
         log.fine("Deleting old binstub $file");
         deleteEntry(file);
       }
     }
   }
 }