Verify that import prefixes don't shadow exports.

tests/language/export_not_shadowed_by_prefix_helper2.dart

Index: tests/language/export_not_shadowed_by_prefix_helper2.dart
diff --git a/runtime/vm/libdart_dependency_helper.cc b/tests/language/export_not_shadowed_by_prefix_helper2.dart
similarity index 57%
copy from runtime/vm/libdart_dependency_helper.cc
copy to tests/language/export_not_shadowed_by_prefix_helper2.dart
index ccf26c829687f4cbbbe80f5c9a074d075613a2be..ae2dca5fcf0a4842b29e20d7652b35b6bfd65cfc 100644
--- a/runtime/vm/libdart_dependency_helper.cc
+++ b/tests/language/export_not_shadowed_by_prefix_helper2.dart
@@ -1,8 +1,9 @@
-// Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
+// Copyright (c) 2016, 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.
 
-int main(int argc, char *argv[]) {
-  return 0;
+void f() {
+  f_called = true;
 }
 
+bool f_called = false;