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

sdk/lib/_internal/pub_generated/lib/src/barback.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS 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 file.
 
 library pub.barback;
 
 import 'package:barback/barback.dart';
 import 'package:path/path.dart' as p;
 import 'package:pub_semver/pub_semver.dart';
 
@@ skipping 33 matching lines @@
 
 /// Converts [id] to a "package:" URI.
 ///
 /// This will throw an [ArgumentError] if [id] doesn't represent a library in
 /// `lib/`.
 Uri idToPackageUri(AssetId id) {
   if (!id.path.startsWith('lib/')) {
     throw new ArgumentError("Asset id $id doesn't identify a library.");
   }
 
-  return new Uri(scheme: 'package',
+  return new Uri(
+      scheme: 'package',
       path: p.url.join(id.package, id.path.replaceFirst('lib/', '')));
 }
 
 /// Converts [uri] into an [AssetId] if its path is within "packages".
 ///
 /// If the URL contains a special directory, but lacks a following package name,
 /// throws a [FormatException].
 ///
 /// If the URI doesn't contain one of those special directories, returns null.
 AssetId packagesUrlToId(Uri url) {
   var parts = p.url.split(url.path);
 
   // Strip the leading "/" from the URL.
   if (parts.isNotEmpty && parts.first == "/") parts = parts.skip(1).toList();
 
   if (parts.isEmpty) return null;
 
   // Check for "packages" in the URL.
   // TODO(rnystrom): If we rewrite "package:" imports to relative imports that
   // point to a canonical "packages" directory, we can limit "packages" to the
   // root of the URL as well. See: #16649.
   var index = parts.indexOf("packages");
   if (index == -1) return null;
 
   // There should be a package name after "packages".
   if (parts.length <= index + 1) {
     throw new FormatException(
-        'Invalid URL path "${url.path}". Expected package name '
-        'after "packages".');
+        'Invalid URL path "${url.path}". Expected package name ' 'after "packages".');
   }
 
   var package = parts[index + 1];
   var assetPath = p.url.join("lib", p.url.joinAll(parts.skip(index + 2)));
   return new AssetId(package, assetPath);
 }