[reference - do not submit] Always create four pools in TaskSchedulerImpl.

base/task_scheduler/scheduler_worker_pool_params.h

 // 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.
 
 #ifndef BASE_TASK_SCHEDULER_SCHEDULER_WORKER_POOL_PARAMS_H_
 #define BASE_TASK_SCHEDULER_SCHEDULER_WORKER_POOL_PARAMS_H_
 
-#include <string>
-
 #include "base/task_scheduler/scheduler_worker_params.h"
-#include "base/threading/platform_thread.h"
 #include "base/time/time.h"
 
 namespace base {
 
 class BASE_EXPORT SchedulerWorkerPoolParams final {
  public:
   enum class StandbyThreadPolicy {
     // Create threads as needed on demand, reclaimed as necessary.
     LAZY,
     // When possible, keep one idle thread alive on standby, reclaimed as
     // necessary.
     ONE,
   };
 
-  // Construct a scheduler worker pool parameter object. |name| will be used to
-  // label the pool's threads ("TaskScheduler" + |name| + index) and histograms
-  // ("TaskScheduler." + histogram name + "." + |name| + extra suffixes). The
-  // pool will contain up to |max_threads|. |priority_hint| is the preferred
-  // thread priority; the actual thread priority depends on shutdown state and
-  // platform capabilities. |standby_thread_policy| indicates whether an idle
+  // Constructs an invalid scheduler worker pool parameter object.
+  SchedulerWorkerPoolParams();
+
+  // Constructs a scheduler worker pool parameter object. The pool will contain
+  // up to |max_threads|. |standby_thread_policy| indicates whether an idle
   // thread should be kept alive on standby. |suggested_reclaim_time| sets a
   // suggestion on when to reclaim idle threads. The pool is free to ignore this
   // value for performance or correctness reasons. |backward_compatibility|
   // indicates whether backward compatibility is enabled.
   SchedulerWorkerPoolParams(
-      const std::string& name,
-      ThreadPriority priority_hint,
       StandbyThreadPolicy standby_thread_policy,
       int max_threads,
       TimeDelta suggested_reclaim_time,
       SchedulerBackwardCompatibility backward_compatibility =
           SchedulerBackwardCompatibility::DISABLED);
+
   SchedulerWorkerPoolParams(const SchedulerWorkerPoolParams& other);
   SchedulerWorkerPoolParams& operator=(const SchedulerWorkerPoolParams& other);
 
-  const std::string& name() const { return name_; }
-  ThreadPriority priority_hint() const { return priority_hint_; }
+  // Returns true if this object can be used to initialize a worker pool.
+  bool IsValid() const;
+
   StandbyThreadPolicy standby_thread_policy() const {
     return standby_thread_policy_;
   }
   size_t max_threads() const { return max_threads_; }
   TimeDelta suggested_reclaim_time() const { return suggested_reclaim_time_; }
   SchedulerBackwardCompatibility backward_compatibility() const {
     return backward_compatibility_;
   }
 
  private:
-  std::string name_;
-  ThreadPriority priority_hint_;
   StandbyThreadPolicy standby_thread_policy_;
   size_t max_threads_;
   TimeDelta suggested_reclaim_time_;
   SchedulerBackwardCompatibility backward_compatibility_;
 };
 
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_SCHEDULER_WORKER_POOL_PARAMS_H_