Update AssertSingletonAllowed log message to reflect new restrictions w.r.t. CONTINUE_ON_SHUTDOWN t…

base/threading/thread_restrictions.cc

Index: base/threading/thread_restrictions.cc
diff --git a/base/threading/thread_restrictions.cc b/base/threading/thread_restrictions.cc
index 00306c5ae7d6c8ea17fcc2170b08b11c15d257ce..c3e672df531bc02f220fed79924dec751f5821e3 100644
--- a/base/threading/thread_restrictions.cc
+++ b/base/threading/thread_restrictions.cc
@@ -56,8 +56,12 @@ void ThreadRestrictions::AssertSingletonAllowed() {
   if (g_singleton_disallowed.Get().Get()) {
     LOG(FATAL) << "LazyInstance/Singleton is not allowed to be used on this "
                << "thread.  Most likely it's because this thread is not "
-               << "joinable, so AtExitManager may have deleted the object "
-               << "on shutdown, leading to a potential shutdown crash.";
+               << "joinable (or the current task is running with "
+               << "TaskShutdownBehavior::CONTINUE_ON_SHUTDOWN semantics), so "
+               << "AtExitManager may have deleted the object on shutdown, "
+               << "leading to a potential shutdown crash. If you need to use "
+               << "the object from this context, it'll have to be updated to "
+               << "use Leaky traits.";
   }
 }