Support directories other than "web" in pub build.

sdk/lib/_internal/pub/test/build/handles_long_paths_test.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.
 
 import 'package:scheduled_test/scheduled_test.dart';
 
 import 'package:path/path.dart' as path;
 
 import '../descriptor.dart' as d;
 import '../test_pub.dart';
@@ skipping 42 matching lines @@
         d.file("index.html", "html"),
       ])
     ]).create();
 
     schedulePub(args: ["build"],
         output: new RegExp(r"Built 2 files!"),
         exitCode: 0);
 
     d.dir(appPath, [
       d.dir('build', [
-        d.file("index.html", "html"),
-        d.dir('assets', [
-          d.dir('foo', [
-            d.file('foo.txt', 'foo')
+        d.dir('web', [
+          d.file("index.html", "html"),
+          d.dir('assets', [
+            d.dir('foo', [
+              d.file('foo.txt', 'foo')
+            ])
           ])
         ])
       ])
     ]).validate();
   });
 }