Make a bunch of stuff in pub synchronous.

utils/pub/system_cache.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.
 
 library system_cache;
 
 import 'dart:io';
 import 'dart:async';
 
 import 'git_source.dart';
@@ skipping 53 matching lines @@
   /// reads it from the cache. Otherwise, requests it from the source.
   Future<Package> describe(PackageId id) {
     Future<Package> getUncached() {
       // Not cached, so get it from the source.
       return id.describe().then((pubspec) => new Package.inMemory(pubspec));
     }
 
     // Try to get it from the system cache first.
     if (id.source.shouldCache) {
       return id.systemCacheDirectory.then((packageDir) {
-        if (!dirExistsSync(packageDir)) return getUncached();
-        return Package.load(id.name, packageDir, sources);
+        if (!dirExists(packageDir)) return getUncached();
+        return new Package(id.name, packageDir, sources);
       });
     }
 
     // Not cached, so get it from the source.
     return getUncached();
   }
 
   /// Ensures that the package identified by [id] is installed to the cache,
   /// loads it, and returns it.
   ///
@@ skipping 12 matching lines @@
     _pendingInstalls[id] = future;
     return future;
   }
 
   /// Create a new temporary directory within the system cache. The system
   /// cache maintains its own temporary directory that it uses to stage
   /// packages into while installing. It uses this instead of the OS's system
   /// temp directory to ensure that it's on the same volume as the pub system
   /// cache so that it can move the directory from it.
   Future<Directory> createTempDir() {
-    return ensureDir(tempDir).then((temp) {
+    return defer(() {
+      var temp = ensureDir(tempDir);
       return io.createTempDir(join(temp, 'dir'));
     });
   }
 
   /// Delete's the system cache's internal temp directory.
   Future deleteTempDir() {
     log.fine('Clean up system cache temp directory $tempDir.');
-    return dirExists(tempDir).then((exists) {
-      if (!exists) return;
+    return defer(() {
+      if (!dirExists(tempDir)) return;
       return deleteDir(tempDir);
     });
   }
 }