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

tools/gn/scheduler.cc

 // Copyright (c) 2013 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 "tools/gn/scheduler.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/command_line.h"
@@ skipping 49 matching lines @@
   //
   // The minimum thread count is based on measuring the optimal threads for the
   // Chrome build on a several-year-old 4-core MacBook.
   int num_cores = GetCPUCount() / 2;  // Almost all CPUs now are hyperthreaded.
   return std::max(num_cores - 1, 8);
 }
 
 }  // namespace
 
 Scheduler::Scheduler()
-    : pool_(new base::SequencedWorkerPool(GetThreadCount(), "worker_")),
+    : pool_(new base::SequencedWorkerPool(GetThreadCount(),
+                                          "worker_",
+                                          base::TaskPriority::USER_VISIBLE)),
       input_file_manager_(new InputFileManager),
       verbose_logging_(false),
       work_count_(0),
       is_failed_(false),
       has_been_shutdown_(false) {
   g_scheduler = this;
 }
 
 Scheduler::~Scheduler() {
   if (!has_been_shutdown_)
@@ skipping 151 matching lines @@
 void Scheduler::DoWork(const base::Closure& closure) {
   closure.Run();
   DecrementWorkCount();
 }
 
 void Scheduler::OnComplete() {
   // Should be called on the main thread.
   DCHECK(base::MessageLoop::current() == main_loop());
   runner_.Quit();
 }