Don't try to get dart2js inputs from barback for directories that aren't public.

sdk/lib/_internal/pub/test/transformer/dart2js/reads_nonpublic_files_from_disk_test.dart

Index: sdk/lib/_internal/pub/test/transformer/dart2js/reads_nonpublic_files_from_disk_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/dart2js/allows_import_in_dart_code_test.dart b/sdk/lib/_internal/pub/test/transformer/dart2js/reads_nonpublic_files_from_disk_test.dart
similarity index 59%
copy from sdk/lib/_internal/pub/test/transformer/dart2js/allows_import_in_dart_code_test.dart
copy to sdk/lib/_internal/pub/test/transformer/dart2js/reads_nonpublic_files_from_disk_test.dart
index eb95620da47bc7cd52d238055088ed25c29bc950..982c45e3adaf74d5730d8c611d82ab9405a52888 100644
--- a/sdk/lib/_internal/pub/test/transformer/dart2js/allows_import_in_dart_code_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/dart2js/reads_nonpublic_files_from_disk_test.dart
@@ -12,22 +12,14 @@ import '../../serve/utils.dart';
 
 main() {
   initConfig();
-  integration("handles imports in the Dart code", () {
-    d.dir("foo", [
-      d.libPubspec("foo", "0.0.1"),
-      d.dir("lib", [
-        d.file("foo.dart", """
-library foo;
-foo() => 'footext';
-""")
-      ])
-    ]).create();
-
+  integration("reads imported files from non-public directories straight from"
+      "the file system", () {
+    // Since the "private" directory isn't served by the barback server, the
+    // relative import for it will fail if the dart2js transformer tries to
+    // get it from barback. This is a regression test for dartbug.com/15688.
     d.dir(appPath, [
-      d.appPubspec({
-        "foo": {"path": "../foo"}
-      }),
-      d.dir("lib", [
+      d.appPubspec(),
+      d.dir("private", [
         d.file("lib.dart", """
 library lib;
 lib() => 'libtext';
@@ -35,18 +27,15 @@ lib() => 'libtext';
       ]),
       d.dir("web", [
         d.file("main.dart", """
-import 'package:foo/foo.dart';
-import 'package:myapp/lib.dart';
+import '../private/lib.dart';
 void main() {
-  print(foo());
   print(lib());
 }
 """)
       ])
     ]).create();
 
-    pubServe(shouldGetFirst: true);
-    requestShouldSucceed("main.dart.js", contains("footext"));
+    pubServe();
     requestShouldSucceed("main.dart.js", contains("libtext"));
     endPubServe();
   });