Add missing IWYU message_loop.h includes.

services/shape_detection/text_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/text_detection_impl_mac.h"
 
 #include "base/command_line.h"
 #include "base/mac/mac_util.h"
 #include "base/mac/scoped_cftyperef.h"
 #include "base/mac/scoped_nsobject.h"
 #include "base/mac/sdk_forward_declarations.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 "ui/gl/gl_switches.h"
 
 namespace shape_detection {
 
 ACTION_P(RunClosure, closure) {
   closure.Run();
 }
@@ skipping 80 matching lines @@
   // Send the image to Detect() and expect the response in callback.
   EXPECT_CALL(*this, Detection(1)).WillOnce(RunClosure(quit_closure));
   impl_.Detect(std::move(handle), width, height,
                base::Bind(&TextDetectionImplMacTest::DetectCallback,
                           base::Unretained(this)));
 
   run_loop.Run();
 }
 
 }  // shape_detection namespace