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

sdk/lib/_internal/pub_generated/test/get/switch_source_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS d.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 d.file.
 
 library pub_tests;
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   initConfig();
   integration('re-gets a package if its source has changed', () {
     servePackages((builder) => builder.serve("foo", "1.2.3"));
 
-    d.dir('foo', [
-      d.libDir('foo', 'foo 0.0.1'),
-      d.libPubspec('foo', '0.0.1')
-    ]).create();
+    d.dir(
+        'foo',
+        [d.libDir('foo', 'foo 0.0.1'), d.libPubspec('foo', '0.0.1')]).create();
 
-    d.appDir({"foo": {"path": "../foo"}}).create();
+    d.appDir({
+      "foo": {
+        "path": "../foo"
+      }
+    }).create();
 
     pubGet();
 
-    d.packagesDir({"foo": "0.0.1"}).validate();
-    d.appDir({"foo": "any"}).create();
+    d.packagesDir({
+      "foo": "0.0.1"
+    }).validate();
+    d.appDir({
+      "foo": "any"
+    }).create();
 
     pubGet();
 
-    d.packagesDir({"foo": "1.2.3"}).validate();
+    d.packagesDir({
+      "foo": "1.2.3"
+    }).validate();
   });
 }