Get rid of unneeded Future.immediate() calls.

utils/pub/validator.dart

Index: utils/pub/validator.dart
diff --git a/utils/pub/validator.dart b/utils/pub/validator.dart
index d3bc0a7d042debf2bbe134c0c81b7b594149c759..5ec0f233f5a808ba6c2a72b4dd68abb0acae1a86 100644
--- a/utils/pub/validator.dart
+++ b/utils/pub/validator.dart
@@ -53,13 +53,8 @@ abstract class Validator {
       new DirectoryValidator(entrypoint)
     ];
 
-    // TODO(nweiz): The sleep 0 here forces us to go async. This works around
-    // 3356, which causes a bug if all validators are (synchronously) using
-    // Future.immediate and an error is thrown before a handler is set up.
-    return sleep(0).then((_) {
-      return Future.wait(
-          validators.mappedBy((validator) => validator.validate()));
-    }).then((_) {
+    return Future.wait(validators.mappedBy((validator) => validator.validate()))
+      .then((_) {
       var errors =
           flatten(validators.mappedBy((validator) => validator.errors));
       var warnings =