Do not take a MessageLoopForIO in the constructor of TaskTrackerPosix.

base/task_scheduler/task_scheduler_impl.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_TASK_SCHEDULER_IMPL_H_
 #define BASE_TASK_SCHEDULER_TASK_SCHEDULER_IMPL_H_
 
 #include <memory>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/callback.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/synchronization/atomic_flag.h"
 #include "base/task_scheduler/scheduler_worker_pool_impl.h"
 #include "base/task_scheduler/sequence.h"
 #include "base/task_scheduler/task_scheduler.h"
+#include "base/task_scheduler/task_tracker.h"
 #include "base/task_scheduler/task_traits.h"
 #include "base/threading/thread.h"
 #include "build/build_config.h"
 
+#if defined(OS_POSIX) && !defined(OS_NACL_SFI)
+#include "base/task_scheduler/task_tracker_posix.h"
+#endif
+
 namespace base {
 
 class HistogramBase;
 
 namespace internal {
 
 class DelayedTaskManager;
 class SchedulerSingleThreadTaskRunnerManager;
-class TaskTracker;
 
 // Default TaskScheduler implementation. This class is thread-safe.
 class BASE_EXPORT TaskSchedulerImpl : public TaskScheduler {
  public:
   // Creates and returns an initialized TaskSchedulerImpl. CHECKs on failure.
   // |name| is used to label threads and histograms. It should identify the
   // component that creates the TaskScheduler. |init_params| contains params to
   // initialize worker pools.
   //
   // Note: The names and priority hints in |init_params| are ignored.
@@ skipping 34 matching lines @@
   // Returns the worker pool that runs Tasks with |traits|.
   SchedulerWorkerPoolImpl* GetWorkerPoolForTraits(
       const TaskTraits& traits) const;
 
   // Callback invoked when a non-single-thread |sequence| isn't empty after a
   // worker pops a Task from it.
   void ReEnqueueSequenceCallback(scoped_refptr<Sequence> sequence);
 
   const std::string name_;
   Thread service_thread_;
-  std::unique_ptr<TaskTracker> task_tracker_;
+#if defined(OS_POSIX) && !defined(OS_NACL_SFI)
+  TaskTrackerPosix task_tracker_;
+#else
+  TaskTracker task_tracker_;
+#endif
   std::unique_ptr<DelayedTaskManager> delayed_task_manager_;
   std::unique_ptr<SchedulerSingleThreadTaskRunnerManager>
       single_thread_task_runner_manager_;
 
   // There are 4 SchedulerWorkerPoolImpl in this array to match the 4
   // SchedulerWorkerPoolParams in TaskScheduler::InitParams.
   std::unique_ptr<SchedulerWorkerPoolImpl> worker_pools_[4];
 
 #if DCHECK_IS_ON()
   // Set once JoinForTesting() has returned.
   AtomicFlag join_for_testing_returned_;
 #endif
 
   DISALLOW_COPY_AND_ASSIGN(TaskSchedulerImpl);
 };
 
 }  // namespace internal
 }  // namespace base
 
 #endif  // BASE_TASK_SCHEDULER_TASK_SCHEDULER_IMPL_H_