Support directories other than "web" in pub build.

sdk/lib/_internal/pub/test/build/copies_non_dart_files_to_build_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("copies non-Dart files to build/", () {
     servePackages([packageMap("browser", "1.0.0")]);
 
     d.dir(appPath, [
       // A browser dependency with no entrypoints shouldn't cause dart.js to be
       // copied in.
       d.appPubspec({"browser": "1.0.0"}),
       d.dir('web', [
         d.file('file.txt', 'contents'),
         d.dir('subdir', [
           d.file('subfile.txt', 'subcontents')
         ])
       ])
     ]).create();
 
     schedulePub(args: ["build"],
-        output: new RegExp(r"Built \d+ files!"),
-        exitCode: 0);
+        output: new RegExp(r"Built 2 files!"));
 
     d.dir(appPath, [
       d.dir('build', [
-        d.nothing('packages'),
-        d.file('file.txt', 'contents'),
-        d.dir('subdir', [
-          d.file('subfile.txt', 'subcontents')
+        d.dir('web', [
+          d.nothing('packages'),
+          d.file('file.txt', 'contents'),
+          d.dir('subdir', [
+            d.file('subfile.txt', 'subcontents')
+          ])
         ])
       ])
     ]).validate();
   });
 }