allow unit_tests to re-create service manager context.

content/browser/child_process_launcher_helper_posix.cc

Index: content/browser/child_process_launcher_helper_posix.cc
diff --git a/content/browser/child_process_launcher_helper_posix.cc b/content/browser/child_process_launcher_helper_posix.cc
index f245ef2f83b9412e30714f6ae8165eae31f59ed4..e655bdcfb391fd693a2c5860ed0102418ea3bc16 100644
--- a/content/browser/child_process_launcher_helper_posix.cc
+++ b/content/browser/child_process_launcher_helper_posix.cc
@@ -141,5 +141,9 @@ void SetFilesToShareForServicePosix(const std::string& service_name,
   GetRequiredFilesByServiceMap()[service_name] = std::move(required_files);
 }
 
+void ResetFilesToShareForTestingPosix() {
+  GetRequiredFilesByServiceMap().clear();
+}
+
 }  // namespace internal
 }  // namespace content