Add Lazy Creation and Thread Detachment Support in the Scheduler Worker Pool

base/task_scheduler/scheduler_worker_stack.cc

Index: base/task_scheduler/scheduler_worker_stack.cc
diff --git a/base/task_scheduler/scheduler_worker_stack.cc b/base/task_scheduler/scheduler_worker_stack.cc
index 7746373aa664123921a1389eb6c30806c89b100e..7996efe5a398e33b4bb13375b926143c5021c9cb 100644
--- a/base/task_scheduler/scheduler_worker_stack.cc
+++ b/base/task_scheduler/scheduler_worker_stack.cc
@@ -16,8 +16,7 @@ SchedulerWorkerStack::SchedulerWorkerStack() = default;
 SchedulerWorkerStack::~SchedulerWorkerStack() = default;
 
 void SchedulerWorkerStack::Push(SchedulerWorker* worker) {
-  DCHECK(std::find(stack_.begin(), stack_.end(), worker) == stack_.end())
-      << "SchedulerWorker already on stack";
+  DCHECK(!Contains(worker)) << "SchedulerWorker already on stack";
   stack_.push_back(worker);
 }
 
@@ -29,6 +28,16 @@ SchedulerWorker* SchedulerWorkerStack::Pop() {
   return worker;
 }
 
+SchedulerWorker* SchedulerWorkerStack::Peek() const {
+  if (IsEmpty())
+    return nullptr;
+  return stack_.back();
+}
+
+bool SchedulerWorkerStack::Contains(const SchedulerWorker* worker) const {
+  return std::find(stack_.begin(), stack_.end(), worker) != stack_.end();
+}
+
 void SchedulerWorkerStack::Remove(const SchedulerWorker* worker) {
   auto it = std::find(stack_.begin(), stack_.end(), worker);
   if (it != stack_.end())