Support directories other than "web" in pub build.

sdk/lib/_internal/pub/test/build/ignores_non_entrypoint_dart_files_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 '../descriptor.dart' as d;
 import '../test_pub.dart';
 
 main() {
   initConfig();
 
   integration("ignores non-entrypoint Dart files", () {
     d.dir(appPath, [
       d.appPubspec(),
       d.dir('web', [
         d.file('file1.dart', 'var main = () => print("hello");'),
         d.file('file2.dart', 'void main(arg1, arg2, arg3) => print("hello");'),
         d.file('file3.dart', 'class Foo { void main() => print("hello"); }'),
         d.file('file4.dart', 'var foo;')
       ])
     ]).create();
 
     schedulePub(args: ["build"],
-        output: new RegExp(r"Built 0 files!"),
-        exitCode: 0);
+        output: new RegExp(r"Built 0 files!"));
 
     d.dir(appPath, [
       d.dir('build', [
-        d.nothing('file1.dart.js'),
-        d.nothing('file1.dart'),
-        d.nothing('file2.dart.js'),
-        d.nothing('file2.dart'),
-        d.nothing('file3.dart.js'),
-        d.nothing('file3.dart'),
-        d.nothing('file4.dart.js'),
-        d.nothing('file4.dart')
+        d.nothing('web')
       ])
     ]).validate();
   });
 }