Make "--no-packages-dir" the default.

test/downgrade/doesnt_change_git_dependencies_test.dart

 // Copyright (c) 2014, 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() {
   integration("doesn't change git dependencies", () {
     ensureGit();
 
     d.git('foo.git', [
       d.libDir('foo'),
       d.libPubspec('foo', '1.0.0')
     ]).create();
 
     d.appDir({
       "foo": {"git": "../foo.git"}
     }).create();
 
-    pubGet();
+    pubGet(args: ["--packages-dir"]);

[nweiz, 2016/09/28 20:01:21]

Why not package root here? Same question for the other git tests.

[Bob Nystrom, 2016/09/29 00:21:26]

We don't have an easy way of testing that a path into the Git cache contains
what we want it to. We'll need to support that eventually when we totally remove
support for "packages" directories, but I didn't want to go through all of that
right now for this ostensibly tiny patch.

 
     d.dir(packagesPath, [
       d.dir('foo', [
         d.file('foo.dart', 'main() => "foo";')
       ])
     ]).validate();
 
     d.git('foo.git', [
       d.libDir('foo', 'foo 2'),
       d.libPubspec('foo', '1.0.0')
     ]).commit();
 
-    pubDowngrade();
+    pubDowngrade(args: ["--packages-dir"]);
 
     d.dir(packagesPath, [
       d.dir('foo', [
         d.file('foo.dart', 'main() => "foo";')
       ])
     ]).validate();
   });
 }