Add missing IWYU message_loop.h includes.

content/renderer/media/webrtc/webrtc_video_capturer_adapter_unittest.cc

 // Copyright 2014 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 <algorithm>
 
 #include "base/bind.h"
+#include "base/message_loop/message_loop.h"
 #include "base/optional.h"
 #include "base/run_loop.h"
 #include "content/child/child_process.h"
 #include "content/renderer/media/webrtc/webrtc_video_capturer_adapter.h"
 #include "gpu/command_buffer/common/mailbox_holder.h"
 #include "media/base/video_frame.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 namespace {
 static void ReleaseMailboxCB(const gpu::SyncToken& sync_token) {}
@@ skipping 173 matching lines @@
 
 TEST_F(WebRtcVideoCapturerAdapterTest, RespectsConstructionTimeContentHint) {
   // Non-screenshare adapter constructed with detail content hint should not
   // adapt before SetContentHint is run.
   TestContentHintResolutionAdaptation(
       false, blink::WebMediaStreamTrack::ContentHintType::kVideoDetail, false,
       blink::WebMediaStreamTrack::ContentHintType::kVideoMotion, true);
 }
 
 }  // namespace content