Update from https://crrev.com/327068

base/test/sequenced_worker_pool_owner.cc

Index: base/test/sequenced_worker_pool_owner.cc
diff --git a/base/test/sequenced_worker_pool_owner.cc b/base/test/sequenced_worker_pool_owner.cc
index f6a0d013011b0b12049ab0a59b3785fc725ced60..4486323344219db6e344ebe8135bd4ae8e922e5b 100644
--- a/base/test/sequenced_worker_pool_owner.cc
+++ b/base/test/sequenced_worker_pool_owner.cc
@@ -43,6 +43,9 @@ void SequencedWorkerPoolOwner::OnHasWork() {
 void SequencedWorkerPoolOwner::WillWaitForShutdown() {
   if (!will_wait_for_shutdown_callback_.is_null()) {
     will_wait_for_shutdown_callback_.Run();
+
+    // Release the reference to the callback to prevent retain cycles.
+    will_wait_for_shutdown_callback_ = Closure();
   }
 }