Replace defer() with Future.of in pub.

utils/tests/pub/version_solver_test.dart

Index: utils/tests/pub/version_solver_test.dart
diff --git a/utils/tests/pub/version_solver_test.dart b/utils/tests/pub/version_solver_test.dart
index 835139a34ccb90bbf482e8d06ca85eff658885f5..94a7c58a4c76c57785887945e003e3b89682eab2 100644
--- a/utils/tests/pub/version_solver_test.dart
+++ b/utils/tests/pub/version_solver_test.dart
@@ -481,13 +481,11 @@ class MockSource extends Source {
       : _packages = <String, Map<Version, Package>>{};
 
   Future<List<Version>> getVersions(String name, String description) {
-    return defer(() => _packages[description].keys.toList());
+    return new Future.of(() => _packages[description].keys.toList());
   }
 
   Future<Pubspec> describe(PackageId id) {
-    return defer(() {
-      return _packages[id.name][id.version].pubspec;
-    });
+    return new Future.of(() => _packages[id.name][id.version].pubspec);
   }
 
   Future<bool> install(PackageId id, String path) {