Delete the NPAPI plugin browsertests.

content/test/plugin/plugin_thread_async_call_test.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 CONTENT_TEST_PLUGIN_PLUGIN_THREAD_ASYNC_CALL_TEST_H_
-#define CONTENT_TEST_PLUGIN_PLUGIN_THREAD_ASYNC_CALL_TEST_H_
-
-#include "content/test/plugin/plugin_test.h"
-
-namespace base {
-class ShadowingAtExitManager;
-}
-
-namespace NPAPIClient {
-
-// This class tests scheduling and unscheduling of async callbacks using
-// NPN_PluginThreadAsyncCall.
-class PluginThreadAsyncCallTest : public PluginTest {
- public:
-  PluginThreadAsyncCallTest(NPP id, NPNetscapeFuncs *host_functions);
-  ~PluginThreadAsyncCallTest() override;
-
-  NPError New(uint16 mode,
-              int16 argc,
-              const char* argn[],
-              const char* argv[],
-              NPSavedData* saved) override;
-
-  NPError Destroy() override;
-
-  void AsyncCall();
-  void OnCallSucceeded();
-  void OnCallCompleted();
-
- private:
-  // base::Thread needs one of these.
-  base::ShadowingAtExitManager* at_exit_manager_;
-
-  DISALLOW_COPY_AND_ASSIGN(PluginThreadAsyncCallTest);
-};
-
-}  // namespace NPAPIClient
-
-#endif  // CONTENT_TEST_PLUGIN_PLUGIN_THREAD_ASYNC_CALL_TEST_H_