Remove calls to MessageLoop::current() in tools.

tools/gn/scheduler.h

 // 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.
 
 #ifndef TOOLS_GN_SCHEDULER_H_
 #define TOOLS_GN_SCHEDULER_H_
 
 #include <map>
 
 #include "base/atomic_ref_count.h"
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
+#include "base/single_thread_task_runner.h"
 #include "base/synchronization/lock.h"
 #include "base/threading/sequenced_worker_pool.h"
 #include "tools/gn/input_file_manager.h"
 #include "tools/gn/label.h"
 #include "tools/gn/source_file.h"
 #include "tools/gn/token.h"
 
 class Target;
 
 // Maintains the thread pool and error state.
 class Scheduler {
  public:
   Scheduler();
   ~Scheduler();
 
   bool Run();
 
-  base::MessageLoop* main_loop() { return &main_loop_; }
+  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(); }
 
   bool verbose_logging() const { return verbose_logging_; }
   void set_verbose_logging(bool v) { verbose_logging_ = v; }
 
   // TODO(brettw) data race on this access (benign?).
   bool is_failed() const { return is_failed_; }
 
@@ skipping 80 matching lines @@
   std::vector<SourceFile> written_files_;
   std::vector<const Target*> write_runtime_deps_targets_;
   std::multimap<SourceFile, const Target*> unknown_generated_inputs_;
 
   DISALLOW_COPY_AND_ASSIGN(Scheduler);
 };
 
 extern Scheduler* g_scheduler;
 
 #endif  // TOOLS_GN_SCHEDULER_H_