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

base/task_scheduler/scheduler_worker_stack.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/task_scheduler/scheduler_worker_stack.h"
 
 #include <algorithm>
 
 #include "base/logging.h"
 
 namespace base {
 namespace internal {
 
 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);
 }
 
 SchedulerWorker* SchedulerWorkerStack::Pop() {
   if (IsEmpty())
     return nullptr;
   SchedulerWorker* const worker = stack_.back();
   stack_.pop_back();
   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())
     stack_.erase(it);
 }
 
 }  // namespace internal
 }  // namespace base