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

base/task_scheduler/scheduler_worker_pool_impl.h

Index: base/task_scheduler/scheduler_worker_pool_impl.h
diff --git a/base/task_scheduler/scheduler_worker_pool_impl.h b/base/task_scheduler/scheduler_worker_pool_impl.h
index 0c1fdcd13a2e71506164efb7abc4dff420f295ea..4617df5496ee4318c819008331253721d634e3cf 100644
--- a/base/task_scheduler/scheduler_worker_pool_impl.h
+++ b/base/task_scheduler/scheduler_worker_pool_impl.h
@@ -25,6 +25,7 @@
 #include "base/task_scheduler/scheduler_worker_stack.h"
 #include "base/task_scheduler/sequence.h"
 #include "base/task_scheduler/task.h"
+#include "base/threading/platform_thread.h"
 #include "base/time/time.h"
 
 namespace base {
@@ -50,13 +51,18 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
   // JoinForTesting() has returned.
   ~SchedulerWorkerPoolImpl() override;
 
-  // Creates a SchedulerWorkerPoolImpl following the |worker_pool_params|
-  // specification. |re_enqueue_sequence_callback| will be invoked after a
-  // worker of this worker pool tries to run a Task. |task_tracker| is used to
-  // handle shutdown behavior of Tasks. |delayed_task_manager| handles Tasks
-  // posted with a delay. Returns nullptr on failure to create a worker pool
-  // with at least one thread.
+  // Creates a SchedulerWorkerPoolImpl. |name| is used to label the pool's
+  // threads ("TaskScheduler" + |name| + index) and histograms ("TaskScheduler."
+  // + histogram name + "." + |name|). |priority_hint| is the preferred thread
+  // priority; the actual thread priority depends on shutdown state and platform
+  // capabilities. |params| contains additional thread creation params.
+  // |re_enqueue_sequence_callback| is invoked after a worker tries to run a
+  // Task. |task_tracker| is used to handle shutdown behavior of Tasks.
+  // |delayed_task_manager| handles Tasks posted with a delay. Returns nullptr
+  // on failure to create a worker pool with at least one thread.
   static std::unique_ptr<SchedulerWorkerPoolImpl> Create(
+      const std::string& name,
+      ThreadPriority priority_hint,
       const SchedulerWorkerPoolParams& params,
       const ReEnqueueSequenceCallback& re_enqueue_sequence_callback,
       TaskTracker* task_tracker,
@@ -109,11 +115,13 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
  private:
   class SchedulerWorkerDelegateImpl;
 
-  SchedulerWorkerPoolImpl(const SchedulerWorkerPoolParams& params,
+  SchedulerWorkerPoolImpl(const std::string& name,
+                          const SchedulerWorkerPoolParams& params,
                           TaskTracker* task_tracker,
                           DelayedTaskManager* delayed_task_manager);
 
   bool Initialize(
+      ThreadPriority priority_hint,
       const SchedulerWorkerPoolParams& params,
       const ReEnqueueSequenceCallback& re_enqueue_sequence_callback);
 
@@ -132,7 +140,7 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
   // Returns true if worker thread detachment is permitted.
   bool CanWorkerDetachForTesting();
 
-  // The name of this worker pool, used to label its worker threads.
+  // The name of this worker pool, used to label threads and histograms.
   const std::string name_;
 
   // All worker owned by this worker pool. Only modified during initialization