First stab at a dev server in pub using barback.

sdk/lib/_internal/pub/test/serve/serve_from_app_asset_test.dart

+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.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 pub_tests;
+
+import 'dart:io';
+
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+
+main() {
+  initConfig();
+  integration("'assets' URLs look in the app's 'asset' directory", () {
+    d.dir(appPath, [
+      d.appPubspec(),
+      d.dir("asset", [
+        d.file("foo.txt", "foo"),
+        d.dir("sub", [
+          d.file("bar.txt", "bar"),
+        ])
+      ])
+    ]).create();
+
+    startPubServe();
+    requestShouldSucceed("assets/myapp/foo.txt", "foo");
+    requestShouldSucceed("assets/myapp/sub/bar.txt", "bar");
+
+    // "assets" can be in a subpath of the URL:
+    requestShouldSucceed("foo/assets/myapp/foo.txt", "foo");
+    requestShouldSucceed("a/b/assets/myapp/sub/bar.txt", "bar");
+    endPubServe();
+  });
+}