Support serving from multiple directories using "pub serve".

sdk/lib/_internal/pub/test/serve/roots/serves_urls_from_custom_roots_test.dart

Index: sdk/lib/_internal/pub/test/serve/roots/serves_urls_from_custom_roots_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/roots/serves_urls_from_custom_roots_test.dart b/sdk/lib/_internal/pub/test/serve/roots/serves_urls_from_custom_roots_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..221b53aab078330b1e24117a893ffb0630b36349
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/serve/roots/serves_urls_from_custom_roots_test.dart
@@ -0,0 +1,32 @@
+// Copyright (c) 2014, 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 'package:path/path.dart' as p;
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../../descriptor.dart' as d;
+import '../../test_pub.dart';
+import '../utils.dart';
+
+main() {
+  initConfig();
+  integration("serves URLs from custom roots", () {
+    d.dir(appPath, [
+      d.appPubspec(),
+      d.dir("example", [
+        d.dir("foo", [d.file("bar", "contents")])
+      ]),
+      d.dir("dir", [d.file("baz", "contents")]),
+      d.dir("web", [d.file("bang", "contents")])
+    ]).create();
+
+    pubServe(args: [p.join("example", "foo"), "dir"]);
+    requestShouldSucceed("bar", "contents", root: p.join("example", "foo"));
+    requestShouldSucceed("baz", "contents", root: "dir");
+    requestShould404("bang", root: "dir");
+    endPubServe();
+  });
+}