Support activating packages from local paths.

sdk/lib/_internal/pub/test/global/activate/path_package_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() {
+  initConfig();
+  integration('activates a package at a local path', () {
+    d.dir("foo", [
+      d.libPubspec("foo", "1.0.0"),
+      d.dir("bin", [
+        d.file("foo.dart", "main() => print('ok');")
+      ])
+    ]).create();
+
+    schedulePub(args: ["global", "activate", "--source", "path", "../foo"],
+        output: "Activated foo 1.0.0.");
+  });
+}