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

tools/gn/header_checker.cc

 // Copyright 2014 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/header_checker.h"
 
 #include <algorithm>
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
@@ skipping 136 matching lines @@
   if (errors_.empty())
     return true;
   *errors = errors_;
   return false;
 }
 
 void HeaderChecker::RunCheckOverFiles(const FileMap& files, bool force_check) {
   if (files.empty())
     return;
 
-  scoped_refptr<base::SequencedWorkerPool> pool(
-      new base::SequencedWorkerPool(16, "HeaderChecker"));
+  scoped_refptr<base::SequencedWorkerPool> pool(new base::SequencedWorkerPool(
+      16, "HeaderChecker", base::TaskPriority::USER_VISIBLE));
   for (const auto& file : files) {
     // Only check C-like source files (RC files also have includes).
     SourceFileType type = GetSourceFileType(file.first);
     if (type != SOURCE_CPP && type != SOURCE_H && type != SOURCE_C &&
         type != SOURCE_M && type != SOURCE_MM && type != SOURCE_RC)
       continue;
 
     // If any target marks it as generated, don't check it. We have to check
     // file_map_, which includes all known files; files only includes those
     // being checked.
@@ skipping 405 matching lines @@
   if (targets_with_other_toolchains.size() +
       targets_with_matching_toolchains.size() > 1)
     msg += "at least one of ";
   msg += "which should somehow be reachable.";
 
   // Danger: must call CreatePersistentRange to put in Err.
   return Err(CreatePersistentRange(source_file, range),
              "Include not allowed.", msg);
 }