Move code that sets up the environment to run a task to TaskTracker::PerformRunTask().

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 24b63e34be90bcd15c618011c946a2af76cca542..1a1977df882e1d6b9eda426f57781ff9038ddd0c 100644
--- a/base/task_scheduler/task_tracker.h
+++ b/base/task_scheduler/task_tracker.h
@@ -77,9 +77,11 @@ class BASE_EXPORT TaskTracker {
   void SetHasShutdownStartedForTesting();
 
  protected:
-  // Runs |task|. An override is expected to call its parent's implementation
-  // but is free to perform extra work before and after doing so.
-  virtual void PerformRunTask(std::unique_ptr<Task> task);
+  // Runs |task|. |sequence_token| is the token identifying the sequence from
+  // which |task| was extracted. An override is expected to call its parent's
+  // implementation but is free to perform extra work before and after doing so.
+  virtual void PerformRunTask(std::unique_ptr<Task> task,
+                              const SequenceToken& sequence_token);
 
 #if DCHECK_IS_ON()
   // Returns true if this context should be exempt from blocking shutdown