Add the ability for a PackageProvider to declare static packages.

pkg/barback/test/static_provider_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.
+
+library barback.test.static_provider_test;
+
+import 'package:scheduled_test/scheduled_test.dart';
+
+import 'utils.dart';
+
+main() {
+  initConfig();
+  test("gets a static source asset", () {
+    initStaticGraph(["app|foo.txt"], staticPackages: ["app"]);
+    expectAsset("app|foo.txt");
+    buildShouldSucceed();
+  });
+
+  test("doesn't get a nonexistent static source asset", () {
+    initStaticGraph(["app|foo.txt"], staticPackages: ["app"]);
+    expectNoAsset("app|bar.txt");
+  });
+
+  test("a transformer can see a static asset", () {
+    initStaticGraph({
+      "static|b.inc": "b",
+      "app|a.txt": "static|b.inc"
+    }, staticPackages: ["static"], transformers: {
+      "app": [[new ManyToOneTransformer("txt")]]
+    });
+    updateSources(["app|a.txt"]);
+    expectAsset("app|a.out", "b");
+  });
+}