Add missing IWYU message_loop.h includes.

components/storage_monitor/storage_monitor_linux_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.
 
 // StorageMonitorLinux unit tests.
 
 #include "components/storage_monitor/storage_monitor_linux.h"
 
 #include <mntent.h>
 #include <stddef.h>
 #include <stdint.h>
 #include <stdio.h>
 
 #include <memory>
 #include <string>
 
 #include "base/files/file_util.h"
 #include "base/files/scoped_temp_dir.h"
 #include "base/logging.h"
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "components/storage_monitor/mock_removable_storage_observer.h"
 #include "components/storage_monitor/removable_device_constants.h"
 #include "components/storage_monitor/storage_info.h"
 #include "components/storage_monitor/storage_monitor.h"
 #include "components/storage_monitor/test_storage_monitor.h"
 #include "content/public/test/test_browser_thread_bundle.h"
 #include "testing/gtest/include/gtest/gtest.h"
@@ skipping 639 matching lines @@
             GetStorageSize(test_path_a));
   EXPECT_EQ(GetDevicePartitionSize(kDeviceNoDCIM),
             GetStorageSize(test_path_b));
   EXPECT_EQ(GetDevicePartitionSize(kInvalidPath),
             GetStorageSize(base::FilePath(kInvalidPath)));
 }
 
 }  // namespace
 
 }  // namespace storage_monitor