TaskScheduler: Make the worker pools of TaskSchedulerImpl configurable

base/task_scheduler/task_scheduler.cc

Index: base/task_scheduler/task_scheduler.cc
diff --git a/base/task_scheduler/task_scheduler.cc b/base/task_scheduler/task_scheduler.cc
index d4a5ca371a20b7486d52ce4440a48da88bae1a08..fd72c12ecd67d11cc3a5fe4aa9e8c40718c0ba43 100644
--- a/base/task_scheduler/task_scheduler.cc
+++ b/base/task_scheduler/task_scheduler.cc
@@ -5,7 +5,6 @@
 #include "base/task_scheduler/task_scheduler.h"
 
 #include "base/logging.h"
-#include "base/task_scheduler/task_scheduler_impl.h"
 
 namespace base {
 
@@ -23,11 +22,6 @@ void TaskScheduler::SetInstance(std::unique_ptr<TaskScheduler> task_scheduler) {
 }
 
 // static
-void TaskScheduler::InitializeDefaultTaskScheduler() {
-  SetInstance(internal::TaskSchedulerImpl::Create());
-}
-
-// static
 TaskScheduler* TaskScheduler::GetInstance() {
   return g_task_scheduler;
 }