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

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 f1070d573b4c36c12fc5b4d731e074ffe96a0736..0d42de9138e39e839e7fcfda892901d1bb0e1eb3 100644
--- a/base/threading/sequenced_worker_pool.h
+++ b/base/threading/sequenced_worker_pool.h
@@ -188,11 +188,13 @@ class BASE_EXPORT SequencedWorkerPool : public TaskRunner {
   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