gn: Remove Scheduler::pool().

InputFileManager used this accessor to post a BLOCK_SHUTDOWN task.
This can be replaced by a call to ScheduleWork(). In both cases,
Scheduler::Run() doesn't return before the task runs.

BUG=

Review-Url: https://codereview.chromium.org/2515383005
Cr-Original-Commit-Position: refs/heads/master@{#436362}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 5476ec6bf7ccbada1734a0cdec7d570bb042aa30

tools/gn/input_file_manager.cc

diff --git a/tools/gn/input_file_manager.cc b/tools/gn/input_file_manager.cc
index c695655..9fd3def 100644
--- a/tools/gn/input_file_manager.cc
+++ b/tools/gn/input_file_manager.cc
@@ -147,9 +147,7 @@
       }
     }
   }
-  g_scheduler->pool()->PostWorkerTaskWithShutdownBehavior(
-      FROM_HERE, schedule_this,
-      base::SequencedWorkerPool::BLOCK_SHUTDOWN);
+  g_scheduler->ScheduleWork(schedule_this);
   return true;
 }
 

tools/gn/scheduler.h

diff --git a/tools/gn/scheduler.h b/tools/gn/scheduler.h
index 67650d8..e20bced 100644
--- a/tools/gn/scheduler.h
+++ b/tools/gn/scheduler.h
@@ -33,7 +33,6 @@
   scoped_refptr<base::SingleThreadTaskRunner> task_runner() {
     return main_loop_.task_runner();
   }
-  base::SequencedWorkerPool* pool() { return pool_.get(); }
 
   InputFileManager* input_file_manager() { return input_file_manager_.get(); }