Automated IWYU fix for TaskRunner includes.

chrome/renderer/chrome_mock_render_thread.h

 // Copyright (c) 2011 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 CHROME_RENDERER_CHROME_MOCK_RENDER_THREAD_H_
 #define CHROME_RENDERER_CHROME_MOCK_RENDER_THREAD_H_
 
 #include <string>
 
 #include "base/macros.h"
+#include "base/single_thread_task_runner.h"
 #include "content/public/test/mock_render_thread.h"
 
 // Extends content::MockRenderThread to know about extension messages.
 class ChromeMockRenderThread : public content::MockRenderThread {
  public:
   ChromeMockRenderThread();
   ~ChromeMockRenderThread() override;
 
   // content::RenderThread overrides.
   scoped_refptr<base::SingleThreadTaskRunner> GetIOTaskRunner() override;
 
   //////////////////////////////////////////////////////////////////////////
   // The following functions are called by the test itself.
 
   void set_io_task_runner(
       const scoped_refptr<base::SingleThreadTaskRunner>& task_runner);
 
  protected:
   scoped_refptr<base::SingleThreadTaskRunner> io_task_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeMockRenderThread);
 };
 
 #endif  // CHROME_RENDERER_CHROME_MOCK_RENDER_THREAD_H_