Add public visibility to pending_task_safety_flag

Bug: b/235812579
Change-Id: I9509fa04317876e0d550e473f0089093afa84a87
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/266145
Commit-Queue: Artem Titov <titovartem@webrtc.org>
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Harald Alvestrand <hta@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#37256}
diff --git a/api/task_queue/BUILD.gn b/api/task_queue/BUILD.gn
index 94b8deb..9c571c5 100644
--- a/api/task_queue/BUILD.gn
+++ b/api/task_queue/BUILD.gn
@@ -107,6 +107,7 @@
 }
 
 rtc_library("pending_task_safety_flag") {
+  visibility = [ "*" ]
   sources = [
     "pending_task_safety_flag.cc",
     "pending_task_safety_flag.h",