Add missing IWYU message_loop.h includes.

chrome/browser/safe_browsing/client_side_detection_host_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 "chrome/browser/safe_browsing/client_side_detection_host.h"
 
 #include <memory>
 #include <tuple>
 #include <utility>
 
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/strings/stringprintf.h"
 #include "base/synchronization/waitable_event.h"
 #include "chrome/browser/safe_browsing/browser_feature_extractor.h"
 #include "chrome/browser/safe_browsing/client_side_detection_service.h"
 #include "chrome/browser/safe_browsing/safe_browsing_service.h"
 #include "chrome/browser/safe_browsing/ui_manager.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/test/base/chrome_render_view_host_test_harness.h"
 #include "chrome/test/base/testing_profile.h"
@@ skipping 1167 matching lines @@
   EXPECT_EQ(url, resource.url);
   EXPECT_EQ(url, resource.original_url);
 
   ExpectStartPhishingDetection(NULL);
 
   // Showing a phishing warning will invalidate all the weak pointers which
   // means we will not extract malware features.
   ExpectShouldClassifyForMalwareResult(false);
 }
 }  // namespace safe_browsing