Support FileDescriptorWatcher in TaskScheduler.

base/task_scheduler/task_tracker.h

Index: base/task_scheduler/task_tracker.h
diff --git a/base/task_scheduler/task_tracker.h b/base/task_scheduler/task_tracker.h
index 8c19456e8772ed04407d5b078f0aad8753b45f37..ff24a2b5a8202d717f7f7b751e4e8848329babfa 100644
--- a/base/task_scheduler/task_tracker.h
+++ b/base/task_scheduler/task_tracker.h
@@ -73,6 +73,12 @@ class BASE_EXPORT TaskTracker {
   // cannot be called after this.
   void SetHasShutdownStartedForTesting();
 
+ protected:
+  // Runs |task|. An override should perform work before running the task,
+  // invoke the base class implementation to run the task and perform work after
+  // running the task.

[gab, 2016/10/21 16:10:48]

An override doesn't "have to" perform work IMO, how about:

// Runs |task|. An override is expected to call its parent's implementation but
is free to perform extra work before and after doing so.

[fdoray, 2016/10/27 13:06:50]

Done.

+  virtual void PerformRunTask(std::unique_ptr<Task> task);
+
  private:
   class State;