Use a direct include of the message_loop header in base/.

base/system_monitor/system_monitor_unittest.cc

 // Copyright (c) 2012 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 "base/system_monitor/system_monitor.h"
 
-#include "base/message_loop.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/test/mock_devices_changed_observer.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace base {
 
 namespace {
 
 class SystemMonitorTest : public testing::Test {
@@ skipping 27 matching lines @@
   RunLoop().RunUntilIdle();
 
   system_monitor_->ProcessDevicesChanged(SystemMonitor::DEVTYPE_UNKNOWN);
   system_monitor_->ProcessDevicesChanged(SystemMonitor::DEVTYPE_UNKNOWN);
   RunLoop().RunUntilIdle();
 }
 
 }  // namespace
 
 }  // namespace base