Add a --[no]-packages-dir flag.

test/no_package_symlinks_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 'package:scheduled_test/scheduled_test.dart';
-
-import 'descriptor.dart' as d;
-import 'test_pub.dart';
-
-main() {
-  forBothPubGetAndUpgrade((command) {
-    group("with --no-package-symlinks", () {
-      integration("installs hosted dependencies to the cache", () {
-        servePackages((builder) {
-          builder.serve("foo", "1.0.0");
-          builder.serve("bar", "1.0.0");
-        });
-
-        d.appDir({"foo": "any", "bar": "any"}).create();
-
-        pubCommand(command, args: ["--no-package-symlinks"]);
-
-        d.nothing("$appPath/packages").validate();
-
-        d.hostedCache([
-          d.dir("foo-1.0.0", [
-            d.dir("lib", [d.file("foo.dart", 'main() => "foo 1.0.0";')])
-          ]),
-          d.dir("bar-1.0.0", [
-            d.dir("lib", [d.file("bar.dart", 'main() => "bar 1.0.0";')])
-          ])
-        ]).validate();
-      });
-
-      integration("installs git dependencies to the cache", () {
-        ensureGit();
-
-        d.git('foo.git', [
-          d.libDir('foo'),
-          d.libPubspec('foo', '1.0.0')
-        ]).create();
-
-        d.appDir({"foo": {"git": "../foo.git"}}).create();
-
-        pubCommand(command, args: ["--no-package-symlinks"]);
-
-        d.nothing("$appPath/packages").validate();
-
-        d.dir(cachePath, [
-          d.dir('git', [
-            d.dir('cache', [d.gitPackageRepoCacheDir('foo')]),
-            d.gitPackageRevisionCacheDir('foo')
-          ])
-        ]).validate();
-      });
-
-      integration("locks path dependencies", () {
-        d.dir("foo", [
-          d.libDir("foo"),
-          d.libPubspec("foo", "0.0.1")
-        ]).create();
-
-        d.dir(appPath, [
-          d.appPubspec({
-            "foo": {"path": "../foo"}
-          })
-        ]).create();
-
-        pubCommand(command, args: ["--no-package-symlinks"]);
-
-        d.nothing("$appPath/packages").validate();
-        d.matcherFile("$appPath/pubspec.lock", contains("foo"));
-      });
-
-      integration("removes package directories near entrypoints", () {
-        d.dir(appPath, [
-          d.appPubspec(),
-          d.dir("packages"),
-          d.dir("bin/packages"),
-          d.dir("web/packages"),
-          d.dir("web/subdir/packages")
-        ]).create();
-
-        pubCommand(command, args: ["--no-package-symlinks"]);
-
-        d.dir(appPath, [
-          d.nothing("packages"),
-          d.nothing("bin/packages"),
-          d.nothing("web/packages"),
-          d.nothing("web/subdir/packages")
-        ]).validate();
-      });
-
-      integration("doesn't remove package directories that pub wouldn't "
-          "generate", () {
-        d.dir(appPath, [
-          d.appPubspec(),
-          d.dir("packages"),
-          d.dir("bin/subdir/packages"),
-          d.dir("lib/packages")
-        ]).create();
-
-        pubCommand(command, args: ["--no-package-symlinks"]);
-
-        d.dir(appPath, [
-          d.nothing("packages"),
-          d.dir("bin/subdir/packages"),
-          d.dir("lib/packages")
-        ]).validate();
-      });
-    });
-  });
-}