pkg/doc_gen: fix test on bots

pkg/docgen/test/only_lib_content_in_pkg_test.dart

Index: pkg/docgen/test/only_lib_content_in_pkg_test.dart
diff --git a/pkg/docgen/test/only_lib_content_in_pkg_test.dart b/pkg/docgen/test/only_lib_content_in_pkg_test.dart
index 6df4a746ef3b8248d65ed85ccca8d34f407aef3c..e429f5f47fde2e47e5c367de7a5e0aa5e52bfd12 100644
--- a/pkg/docgen/test/only_lib_content_in_pkg_test.dart
+++ b/pkg/docgen/test/only_lib_content_in_pkg_test.dart
@@ -27,11 +27,10 @@ void main() {
       expect(p.basename(thisPath), 'only_lib_content_in_pkg_test.dart');
       expect(p.dirname(thisPath), endsWith('test'));
 
-
       var codeDir = p.normalize(p.join(thisPath, '..', '..'));
-      print(codeDir);
       expect(FileSystemEntity.isDirectorySync(codeDir), isTrue);
-      return dg.docgen(['$codeDir/'], out: p.join(d.defaultRoot, 'docs'));
+      return dg.docgen(['$codeDir/'], out: p.join(d.defaultRoot, 'docs'),
+          packageRoot: Platform.packageRoot);
     });
 
     d.dir('docs', [