Move Task Scheduler Single Thread Task Runners to Dedicated Threads

base/task_scheduler/task_scheduler_impl.cc

Index: base/task_scheduler/task_scheduler_impl.cc
diff --git a/base/task_scheduler/task_scheduler_impl.cc b/base/task_scheduler/task_scheduler_impl.cc
index f727c8c3b176eb74a21b49ae87b6b96984d3adfb..90b36dc2c7f4084c40326eb43f2ed91b08388889 100644
--- a/base/task_scheduler/task_scheduler_impl.cc
+++ b/base/task_scheduler/task_scheduler_impl.cc
@@ -10,6 +10,7 @@
 #include "base/bind_helpers.h"
 #include "base/memory/ptr_util.h"
 #include "base/task_scheduler/delayed_task_manager.h"
+#include "base/task_scheduler/scheduler_single_thread_worker_pool_manager.h"
 #include "base/task_scheduler/scheduler_worker_pool_params.h"
 #include "base/task_scheduler/sequence_sort_key.h"
 #include "base/task_scheduler/task.h"
@@ -66,8 +67,8 @@ TaskSchedulerImpl::CreateSequencedTaskRunnerWithTraits(
 scoped_refptr<SingleThreadTaskRunner>
 TaskSchedulerImpl::CreateSingleThreadTaskRunnerWithTraits(
     const TaskTraits& traits) {
-  return GetWorkerPoolForTraits(traits)->CreateSingleThreadTaskRunnerWithTraits(
-      traits);
+  return scheduler_single_thread_worker_pool_manager_
+      ->CreateSingleThreadTaskRunnerWithTraits(traits);
 }
 
 std::vector<const HistogramBase*> TaskSchedulerImpl::GetHistograms() const {
@@ -97,6 +98,7 @@ void TaskSchedulerImpl::JoinForTesting() {
     worker_pool->DisallowWorkerDetachmentForTesting();
   for (const auto& worker_pool : worker_pools_)
     worker_pool->JoinForTesting();
+  scheduler_single_thread_worker_pool_manager_->JoinForTesting();
   service_thread_.Stop();
 #if DCHECK_IS_ON()
   join_for_testing_returned_.Set();
@@ -143,6 +145,11 @@ void TaskSchedulerImpl::Initialize(
   delayed_task_manager_ =
       base::MakeUnique<DelayedTaskManager>(service_thread_.task_runner());
 
+  scheduler_single_thread_worker_pool_manager_ =
+      base::MakeUnique<SchedulerSingleThreadWorkerPoolManager>(
+          worker_pool_params_vector, worker_pool_index_for_traits_callback_,
+          task_tracker_.get(), delayed_task_manager_.get());
+
   // Callback invoked by workers to re-enqueue a sequence in the appropriate
   // PriorityQueue.
   const SchedulerWorkerPoolImpl::ReEnqueueSequenceCallback