Add missing IWYU message_loop.h includes.

third_party/WebKit/public/platform/scheduler/test/fake_renderer_scheduler.h

 // 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.
 
 #ifndef THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_TEST_FAKE_RENDERER_SCHEDULER_H_
 #define THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_TEST_FAKE_RENDERER_SCHEDULER_H_
 
 #include "base/macros.h"
+#include "base/message_loop/message_loop.h"
 #include "public/platform/scheduler/renderer/renderer_scheduler.h"
 
 namespace blink {
 namespace scheduler {
 
 class FakeRendererScheduler : public RendererScheduler {
  public:
   FakeRendererScheduler();
   ~FakeRendererScheduler() override;
 
@@ skipping 40 matching lines @@
       base::TimeDelta main_thread_responsiveness_threshold) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(FakeRendererScheduler);
 };
 
 }  // namespace scheduler
 }  // namespace blink
 
 #endif  // THIRD_PARTY_WEBKIT_PUBLIC_PLATFORM_SCHEDULER_TEST_FAKE_RENDERER_SCHEDULER_H_