[SyncFS] Use nullptr instead of NULL

chrome/browser/sync_file_system/drive_backend/task_dependency_manager_unittest.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 "chrome/browser/sync_file_system/drive_backend/task_dependency_manager.h"
 
 #include "base/files/file_path.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 #define FPL(path) FILE_PATH_LITERAL(path)
@@ skipping 91 matching lines @@
   EXPECT_FALSE(InsertPath(&manager, "app_id", FPL("/foo/bar")));
   EraseExclusiveTask(&manager);
 
   EXPECT_TRUE(InsertPath(&manager, "app_id", FPL("/foo/bar")));
   ErasePath(&manager, "app_id", FPL("/foo/bar"));
 }
 
 TEST(TaskDependencyManagerTest, PermissiveTask) {
   TaskDependencyManager manager;
 
-  EXPECT_TRUE(manager.Insert(NULL));
+  EXPECT_TRUE(manager.Insert(nullptr));
   EXPECT_TRUE(InsertPath(&manager, "app_id", FPL("/foo/bar")));
   EXPECT_FALSE(InsertExclusiveTask(&manager));
   ErasePath(&manager, "app_id", FPL("/foo/bar"));
 
   EXPECT_FALSE(InsertExclusiveTask(&manager));
-  manager.Erase(NULL);
+  manager.Erase(nullptr);
   EXPECT_TRUE(InsertExclusiveTask(&manager));
 
-  EXPECT_FALSE(manager.Insert(NULL));
+  EXPECT_FALSE(manager.Insert(nullptr));
 
   EraseExclusiveTask(&manager);
 }
 
 }  // namespace drive_backend
 }  // namespace sync_file_system