Add TaskPriority as a parameter to SequencedWorkerPool in preparation for TaskScheduler experiment.

base/threading/sequenced_worker_pool.h

Index: base/threading/sequenced_worker_pool.h
diff --git a/base/threading/sequenced_worker_pool.h b/base/threading/sequenced_worker_pool.h
index cbec39561a40db6fd5d3e773907a0642428d4bcf..e1f3e9b2ffcee4b25cf1fd71189a119843f4017f 100644
--- a/base/threading/sequenced_worker_pool.h
+++ b/base/threading/sequenced_worker_pool.h
@@ -17,6 +17,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/single_thread_task_runner.h"
 #include "base/task_runner.h"
+#include "base/task_scheduler/task_traits.h"
 
 namespace tracked_objects {
 class Location;
@@ -187,13 +188,17 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
 
   // Pass the maximum number of threads (they will be lazily created as needed)
   // and a prefix for the thread name to aid in debugging.
+  // |task_priority| will be used to hint base::TaskScheduler for an experiment
+  // in which all SequencedWorkerPool tasks will be redirected to it.
   SequencedWorkerPool(size_t max_threads,
-                      const std::string& thread_name_prefix);
+                      const std::string& thread_name_prefix,
+                      base::TaskPriority task_priority);
 
   // Like above, but with |observer| for testing.  Does not take ownership of
   // |observer|.
   SequencedWorkerPool(size_t max_threads,
                       const std::string& thread_name_prefix,
+                      base::TaskPriority task_priority,
                       TestingObserver* observer);
 
   // Returns the sequence token associated with the given name. Calling this