Move Task Scheduler Single Thread Task Runners to Dedicated Threads

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 3205dae7d1a25d6a0034ba11cc6d7f0ca9562f02..9668ab1b95f7847f660832cdc6bded921d45f03a 100644
--- a/base/task_scheduler/scheduler_worker_pool_impl.h
+++ b/base/task_scheduler/scheduler_worker_pool_impl.h
@@ -45,6 +45,10 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
   // from it.
   using ReEnqueueSequenceCallback = Callback<void(scoped_refptr<Sequence>)>;
 
+  // Callback invoked during destruction of a SingleThreadTaskRunner.
+  using UnregisterSingleThreadWorkerPoolCallback =
+      Callback<void(const SchedulerWorkerPoolImpl* scheduler_worker_pool)>;
+
   // Destroying a SchedulerWorkerPoolImpl returned by Create() is not allowed in
   // production; it is always leaked. In tests, it can only be destroyed after
   // JoinForTesting() has returned.
@@ -62,6 +66,13 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
       TaskTracker* task_tracker,
       DelayedTaskManager* delayed_task_manager);
 
+  static std::unique_ptr<SchedulerWorkerPoolImpl> CreateSingleThreadWorkerPool(
+      const SchedulerWorkerPoolParams& params,
+      UnregisterSingleThreadWorkerPoolCallback
+          unregister_single_thread_worker_callback,
+      TaskTracker* task_tracker,
+      DelayedTaskManager* delayed_task_manager);
+
   // SchedulerWorkerPool:
   scoped_refptr<TaskRunner> CreateTaskRunnerWithTraits(
       const TaskTraits& traits) override;
@@ -109,9 +120,20 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
   class SchedulerSingleThreadTaskRunner;
   class SchedulerWorkerDelegateImpl;
 
+  static std::unique_ptr<SchedulerWorkerPoolImpl> CreateInternal(
+      const SchedulerWorkerPoolParams& params,
+      TaskTracker* task_tracker,
+      DelayedTaskManager* delayed_task_manager,
+      const ReEnqueueSequenceCallback& re_enqueue_sequence_callback,
+      UnregisterSingleThreadWorkerPoolCallback
+          unregister_single_thread_worker_callback);
+
   SchedulerWorkerPoolImpl(const SchedulerWorkerPoolParams& params,
                           TaskTracker* task_tracker,
-                          DelayedTaskManager* delayed_task_manager);
+                          DelayedTaskManager* delayed_task_manager,
+                          UnregisterSingleThreadWorkerPoolCallback
+                              unregister_single_thread_worker_pool_callback =
+                                  UnregisterSingleThreadWorkerPoolCallback());
 
   bool Initialize(
       const SchedulerWorkerPoolParams& params,
@@ -199,6 +221,9 @@ class BASE_EXPORT SchedulerWorkerPoolImpl : public SchedulerWorkerPool {
   TaskTracker* const task_tracker_;
   DelayedTaskManager* const delayed_task_manager_;
 
+  const UnregisterSingleThreadWorkerPoolCallback
+      unregister_single_thread_worker_pool_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(SchedulerWorkerPoolImpl);
 };