Remove calls to deprecated MessageLoop methods in tools.

tools/gn/setup.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/setup.h"
 
 #include <stdlib.h>
 #include <algorithm>
 #include <sstream>
 #include <utility>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/process/launch.h"
+#include "base/single_thread_task_runner.h"
 #include "base/strings/string_split.h"
 #include "base/strings/string_util.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "build/build_config.h"
 #include "tools/gn/commands.h"
 #include "tools/gn/filesystem_utils.h"
 #include "tools/gn/input_file.h"
 #include "tools/gn/parse_tree.h"
 #include "tools/gn/parser.h"
@@ skipping 108 matching lines @@
     return base::FilePath();  // Got to the top.
 
   return FindDotFile(up_one_dir);
 }
 
 // Called on any thread. Post the item to the builder on the main thread.
 void ItemDefinedCallback(base::MessageLoop* main_loop,
                          scoped_refptr<Builder> builder,
                          std::unique_ptr<Item> item) {
   DCHECK(item);
-  main_loop->PostTask(FROM_HERE, base::Bind(&Builder::ItemDefined, builder,
-                                            base::Passed(&item)));
+  main_loop->task_runner()->PostTask(
+      FROM_HERE,
+      base::Bind(&Builder::ItemDefined, builder, base::Passed(&item)));
 }
 
 void DecrementWorkCount() {
   g_scheduler->DecrementWorkCount();
 }
 
 #if defined(OS_WIN)
 
 // Given the path to a batch file that runs Python, extracts the name of the
 // executable actually implementing Python. Generally people write a batch file
@@ skipping 574 matching lines @@
       if (err.has_error()) {
         err.PrintToStdout();
         return false;
       }
     }
     build_settings_.set_exec_script_whitelist(std::move(whitelist));
   }
 
   return true;
 }