Remove support for the special "assets" directory.

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 15 matching lines @@
   // This test ensures that we're normalizing at some point before we throw the
   // path at the OS to choke on.
 
   integration("handles long relative paths", () {
     // Dart2js can take a long time to compile dart code, so we increase the
     // timeout to cope with that.
     currentSchedule.timeout *= 3;
 
     d.dir("some_long_dependency_name", [
       d.libPubspec("foo", "0.0.1"),
-      d.dir("asset", [
+      d.dir("lib", [
         d.file("foo.txt", "foo")
       ])
     ]).create();
 
     // Build a 2,800 character (non-canonicalized) path.
     var longPath = "";
     for (var i = 0; i < 100; i++)
     {
       longPath = path.join(longPath, "..", "some_long_dependency_name");
     }
 
     d.dir(appPath, [
       d.appPubspec({
         "foo": {"path": longPath}
       }),
       d.dir("web", [
         d.file("index.html", "html"),
       ])
     ]).create();
 
     schedulePub(args: ["build"],
         output: new RegExp(r'Built 2 files to "build".'));
 
     d.dir(appPath, [
       d.dir('build', [
         d.dir('web', [
           d.file("index.html", "html"),
-          d.dir('assets', [
+          d.dir('packages', [
             d.dir('foo', [
               d.file('foo.txt', 'foo')
             ])
           ])
         ])
       ])
     ]).validate();
   });
 }