Warn when serving an asset from "asset".

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

Index: sdk/lib/_internal/pub/test/serve/warns_on_serve_from_asset_test.dart
diff --git a/sdk/lib/_internal/pub/test/serve/warns_on_serve_from_asset_test.dart b/sdk/lib/_internal/pub/test/serve/warns_on_serve_from_asset_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..2f4fc497cbccd8a95ad10a801745162073c7f3a5
--- /dev/null
+++ b/sdk/lib/_internal/pub/test/serve/warns_on_serve_from_asset_test.dart
@@ -0,0 +1,56 @@
+// Copyright (c) 2013, 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 pub_tests;
+
+import 'package:scheduled_test/scheduled_stream.dart';
+
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+
+main() {
+  initConfig();
+  integration("warns if an asset from the entrypoint package's 'asset' "
+      "directory is requested", () {
+    d.dir(appPath, [
+      d.appPubspec(),
+      d.dir("asset", [
+        d.file("file.txt", "body")
+      ])
+    ]).create();
+
+    var pub = pubServe();
+    requestShouldSucceed("assets/myapp/file.txt", "body");
+
+    pub.stderr.expect(consumeThrough(emitsLines('''
+Warning: Support for the "asset" directory is deprecated and will be removed soon.
+Please move "asset/file.txt" to "lib/file.txt".''')));
+    endPubServe();
+  });
+
+  integration("warns if an asset from a dependency's 'asset' directory is "
+      "requested", () {
+    d.dir("foo", [
+      d.libPubspec("foo", "0.0.1"),
+      d.dir("asset", [
+        d.file("file.txt", "body")
+      ])
+    ]).create();
+
+    d.dir(appPath, [
+      d.appPubspec({
+        "foo": {"path": "../foo"}
+      })
+    ]).create();
+
+    var pub = pubServe(shouldGetFirst: true);
+    requestShouldSucceed("assets/foo/file.txt", "body");
+
+    pub.stderr.expect(consumeThrough(emitsLines('''
+Warning: Support for the "asset" directory is deprecated and will be removed soon.
+Please ask the maintainer of "foo" to move "asset/file.txt" to "lib/file.txt".''')));
+    endPubServe();
+  });
+}