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

net/ssl/ssl_platform_key_task_runner.cc

 // Copyright 2015 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.
 
 #include "base/lazy_instance.h"
 #include "net/ssl/ssl_platform_key_task_runner.h"
 
 namespace net {
 
 SSLPlatformKeyTaskRunner::SSLPlatformKeyTaskRunner() {
-  worker_pool_ = new base::SequencedWorkerPool(1, "Platform Key Thread");
+  worker_pool_ = new base::SequencedWorkerPool(
+      1, "Platform Key Thread", base::TaskPriority::USER_BLOCKING);
   task_runner_ = worker_pool_->GetSequencedTaskRunnerWithShutdownBehavior(
       worker_pool_->GetSequenceToken(),
       base::SequencedWorkerPool::CONTINUE_ON_SHUTDOWN);
 }
 
 SSLPlatformKeyTaskRunner::~SSLPlatformKeyTaskRunner() {}
 
 scoped_refptr<base::SequencedTaskRunner>
 SSLPlatformKeyTaskRunner::task_runner() {
   return task_runner_;
 }
 
 base::LazyInstance<SSLPlatformKeyTaskRunner>::Leaky g_platform_key_task_runner =
     LAZY_INSTANCE_INITIALIZER;
 
 scoped_refptr<base::SequencedTaskRunner> GetSSLPlatformKeyTaskRunner() {
   return g_platform_key_task_runner.Get().task_runner();
 }
 
 }  // namespace net