Replace PluginThreadTaskRunner with a simpler MainPluginThreadTaskRunner.

remoting/client/plugin/pepper_plugin_thread_delegate.h

-// Copyright (c) 2012 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 REMOTING_CLIENT_PLUGIN_PEPPER_PLUGIN_THREAD_DELEGATE_H_
-#define REMOTING_CLIENT_PLUGIN_PEPPER_PLUGIN_THREAD_DELEGATE_H_
-
-#include "remoting/base/plugin_thread_task_runner.h"
-
-namespace pp {
-class Core;
-}  // namespace pp
-
-namespace remoting {
-
-class PepperPluginThreadDelegate : public PluginThreadTaskRunner::Delegate {
- public:
-  PepperPluginThreadDelegate();
-  ~PepperPluginThreadDelegate() override;
-
-  bool RunOnPluginThread(base::TimeDelta delay,
-                         void(CDECL function)(void*),
-                         void* data) override;
-
- private:
-  pp::Core* core_;
-};
-
-} // namespace remoting
-
-#endif  // REMOTING_CLIENT_PLUGIN_PEPPER_PLUGIN_THREAD_DELEGATE_H_