Revert "gn: Remove Scheduler::pool()."

tools/gn/input_file_manager.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/input_file_manager.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/stl_util.h"
@@ skipping 129 matching lines @@
         // Can just directly issue the callback on the background thread.
         schedule_this = base::Bind(&InvokeFileLoadCallback, callback,
                                    data->parsed_root.get());
       } else {
         // Load is pending on this file, schedule the invoke.
         data->scheduled_callbacks.push_back(callback);
         return true;
       }
     }
   }
-  g_scheduler->ScheduleWork(schedule_this);
+  g_scheduler->pool()->PostWorkerTaskWithShutdownBehavior(
+      FROM_HERE, schedule_this,
+      base::SequencedWorkerPool::BLOCK_SHUTDOWN);
   return true;
 }
 
 const ParseNode* InputFileManager::SyncLoadFile(
     const LocationRange& origin,
     const BuildSettings* build_settings,
     const SourceFile& file_name,
     Err* err) {
   base::AutoLock lock(lock_);
 
@@ skipping 152 matching lines @@
 
   // Run pending invocations. Theoretically we could schedule each of these
   // separately to get some parallelism. But normally there will only be one
   // item in the list, so that's extra overhead and complexity for no gain.
   if (success) {
     for (const auto& cb : callbacks)
       cb.Run(unowned_root);
   }
   return success;
 }