Also makes native theme accesses thread-safe to avoid a race condition when modifying the theme off the UI thread. Since drawable loading can occur off the UI thread, we need to ensure Theme access is thread-safe anyway. This reverts commit c12ec70def2a5682c6cd7fdb3adaa82cc34d5bf6. Change-Id: If8fecde76d62738a8e55eddf898eafc468afdba2