Allow package: imports inside isolates

tests/standalone/package/test_folder/packages/folder_lib.dart

Index: tests/standalone/package/test_folder/packages/folder_lib.dart
diff --git a/lib/html/dartium/nativewrappers.dart b/tests/standalone/package/test_folder/packages/folder_lib.dart
similarity index 62%
copy from lib/html/dartium/nativewrappers.dart
copy to tests/standalone/package/test_folder/packages/folder_lib.dart
index 44ab39e1ac7567e620f8402b566e4b492836d41e..006fe7150965f4f8e8e78f32ff556b6485f4d8ca 100644
--- a/lib/html/dartium/nativewrappers.dart
+++ b/tests/standalone/package/test_folder/packages/folder_lib.dart
@@ -2,7 +2,8 @@
 // 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('nativewrappers');
+library folder_lib;
 
-class NativeFieldWrapperClass1 {
-}
+// This is a library that's available to folder_isolate.dart
+// but not package_isolate_test.dart
+int count = 0;