Add a TaskPriority cap to the SWP redirection to experiment with no redirections at USER_BLOCKING.

base/threading/sequenced_worker_pool.h

 // Copyright (c) 2012 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_THREADING_SEQUENCED_WORKER_POOL_H_
 #define BASE_THREADING_SEQUENCED_WORKER_POOL_H_
 
 #include <stddef.h>
 
 #include <cstddef>
@@ skipping 170 matching lines @@
   // Returns a unique token that can be used to sequence tasks posted to
   // PostSequencedWorkerTask(). Valid tokens are always nonzero.
   static SequenceToken GetSequenceToken();
 
   // Enables posting tasks to this process' SequencedWorkerPools. Cannot be
   // called if already enabled. This is not thread-safe; proper synchronization
   // is required to use any SequencedWorkerPool method after calling this.
   static void EnableForProcess();
 
   // Same as EnableForProcess(), but tasks are redirected to the registered
-  // TaskScheduler. There must be a registered TaskScheduler when this is
+  // TaskScheduler. All redirections' TaskPriority will be capped to
+  // |max_task_priority|. There must be a registered TaskScheduler when this is
   // called.
   // TODO(gab): Remove this if http://crbug.com/622400 fails
   // (SequencedWorkerPool will be phased out completely otherwise).
-  static void EnableWithRedirectionToTaskSchedulerForProcess();
+  static void EnableWithRedirectionToTaskSchedulerForProcess(
+      TaskPriority max_task_priority = TaskPriority::HIGHEST);
 
   // Disables posting tasks to this process' SequencedWorkerPools. Calling this
   // while there are active SequencedWorkerPools is not supported. This is not
   // thread-safe; proper synchronization is required to use any
   // SequencedWorkerPool method after calling this.
   static void DisableForProcessForTesting();
 
   // Returns true if posting tasks to this process' SequencedWorkerPool is
   // enabled (with or without redirection to TaskScheduler).
   static bool IsEnabled();
@@ skipping 201 matching lines @@
   // Avoid pulling in too many headers by putting (almost) everything
   // into |inner_|.
   const std::unique_ptr<Inner> inner_;
 
   DISALLOW_COPY_AND_ASSIGN(SequencedWorkerPool);
 };
 
 }  // namespace base
 
 #endif  // BASE_THREADING_SEQUENCED_WORKER_POOL_H_