Revert "Use native async/await support in pub."

sdk/lib/_internal/pub_generated/test/downgrade/dry_run_does_not_apply_changes_test.dart

Index: sdk/lib/_internal/pub_generated/test/downgrade/dry_run_does_not_apply_changes_test.dart
diff --git a/sdk/lib/_internal/pub/test/downgrade/dry_run_does_not_apply_changes_test.dart b/sdk/lib/_internal/pub_generated/test/downgrade/dry_run_does_not_apply_changes_test.dart
similarity index 75%
copy from sdk/lib/_internal/pub/test/downgrade/dry_run_does_not_apply_changes_test.dart
copy to sdk/lib/_internal/pub_generated/test/downgrade/dry_run_does_not_apply_changes_test.dart
index c1f8335c1ba0e1f414012370d14474e2f6a2a040..3b0c9d1e4a4e17d31a5a6cdd998829c2908b8bb2 100644
--- a/sdk/lib/_internal/pub/test/downgrade/dry_run_does_not_apply_changes_test.dart
+++ b/sdk/lib/_internal/pub_generated/test/downgrade/dry_run_does_not_apply_changes_test.dart
@@ -35,16 +35,14 @@ main() {
     });
 
     // Do the dry run.
-    pubDowngrade(args: ["--dry-run"], output: allOf([
-      contains("< foo 1.0.0"),
-      contains("Would change 1 dependency.")
-    ]));
+    pubDowngrade(
+        args: ["--dry-run"],
+        output: allOf(
+            [contains("< foo 1.0.0"), contains("Would change 1 dependency.")]));
 
-    d.dir(appPath, [
-      // The lockfile should be unmodified.
+    d.dir(appPath, [// The lockfile should be unmodified.
       d.matcherFile("pubspec.lock", contains("2.0.0")),
-      // The "packages" directory should not have been regenerated.
-      d.nothing("packages")
-    ]).validate();
+          // The "packages" directory should not have been regenerated.
+      d.nothing("packages")]).validate();
   });
 }