Add missing IWYU message_loop.h includes.

content/browser/compositor/reflector_impl_unittest.cc

 // Copyright 2015 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 "content/browser/compositor/reflector_impl.h"
 
 #include "base/callback.h"
 #include "base/memory/ptr_util.h"
+#include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "base/single_thread_task_runner.h"
 #include "build/build_config.h"
 #include "cc/output/output_surface_frame.h"
 #include "cc/scheduler/begin_frame_source.h"
 #include "cc/scheduler/delay_based_time_source.h"
 #include "cc/test/test_context_provider.h"
 #include "cc/test/test_web_graphics_context_3d.h"
 #include "components/display_compositor/compositor_overlay_candidate_validator.h"
 #include "content/browser/compositor/browser_compositor_output_surface.h"
@@ skipping 215 matching lines @@
   plane_2.plane_z_order = 1;
   list.push_back(plane_1);
   list.push_back(plane_2);
   output_surface_->GetOverlayCandidateValidator()->CheckOverlaySupport(&list);
   EXPECT_FALSE(list[0].overlay_handled);
 }
 #endif  // defined(USE_OZONE)
 
 }  // namespace
 }  // namespace content