Make a bunch of stuff in pub synchronous.

utils/pub/validator/directory.dart

Index: utils/pub/validator/directory.dart
diff --git a/utils/pub/validator/directory.dart b/utils/pub/validator/directory.dart
index 09a6c7e952b713e94a8f5e103bdf59530693437c..6ab932ca64224ac591826a9de4c575231545093c 100644
--- a/utils/pub/validator/directory.dart
+++ b/utils/pub/validator/directory.dart
@@ -8,6 +8,7 @@ import 'dart:async';
 
 import '../entrypoint.dart';
 import '../io.dart';
+import '../utils.dart';
 import '../validator.dart';
 
 /// A validator that validates a package's top-level directories.
@@ -19,29 +20,27 @@ class DirectoryValidator extends Validator {
 
   Future validate() {
     return listDir(entrypoint.root.dir).then((dirs) {
-      return Future.wait(dirs.map((dir) {
-        return dirExists(dir).then((exists) {
-          if (!exists) return;
-
-          dir = basename(dir);
-          if (_PLURAL_NAMES.contains(dir)) {
-            // Cut off the "s"
-            var singularName = dir.substring(0, dir.length - 1);
-            warnings.add('Rename the top-level "$dir" directory to '
-                    '"$singularName".\n'
-                'The Pub layout convention is to use singular directory '
-                    'names.\n'
-                'Plural names won\'t be correctly identified by Pub and other '
-                    'tools.');
-          }
-
-          if (dir.contains(new RegExp(r"^samples?$"))) {
-            warnings.add('Rename the top-level "$dir" directory to "example".\n'
-                'This allows Pub to find your examples and create "packages" '
-                    'directories for them.\n');
-          }
-        });
-      }));
+      for (var dir in dirs) {
+        if (!dirExists(dir)) continue;
+
+        dir = basename(dir);
+        if (_PLURAL_NAMES.contains(dir)) {
+          // Cut off the "s"
+          var singularName = dir.substring(0, dir.length - 1);
+          warnings.add('Rename the top-level "$dir" directory to '
+                  '"$singularName".\n'
+              'The Pub layout convention is to use singular directory '
+                  'names.\n'
+              'Plural names won\'t be correctly identified by Pub and other '
+                  'tools.');
+        }
+
+        if (dir.contains(new RegExp(r"^samples?$"))) {
+          warnings.add('Rename the top-level "$dir" directory to "example".\n'
+              'This allows Pub to find your examples and create "packages" '
+                  'directories for them.\n');
+        }
+      }
     });
   }
 }