Add missing IWYU message_loop.h includes.

services/shape_detection/face_detection_impl_mac_unittest.mm

 // Copyright 2017 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 "services/shape_detection/face_detection_impl_mac.h"
 
 #include "base/base64.h"
 #include "base/command_line.h"
 #include "base/mac/scoped_nsobject.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "ui/gfx/codec/jpeg_codec.h"
 #include "ui/gl/gl_switches.h"
 
 using ::testing::TestWithParam;
 using ::testing::ValuesIn;
 
@@ skipping 79 matching lines @@
   impl_->Detect(std::move(handle), size.width(), size.height(),
                 base::Bind(&FaceDetectionImplMacTest::DetectCallback,
                            base::Unretained(this)));
 
   run_loop.Run();
 }
 
 INSTANTIATE_TEST_CASE_P(, FaceDetectionImplMacTest, ValuesIn({true, false}));
 
 }  // shape_detection namespace