Delete the NPAPI plugin browsertests.

content/test/plugin/plugin_private_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_PRIVATE_TEST_H_
-#define CONTENT_TEST_PLUGIN_PLUGIN_PRIVATE_TEST_H_
-
-#include "base/compiler_specific.h"
-#include "content/test/plugin/plugin_test.h"
-
-namespace NPAPIClient {
-
-// The PluginPrivateTest tests that a plugin can query if the browser is in
-// private browsing mode.
-class PrivateTest : public PluginTest {
- public:
-  PrivateTest(NPP id, NPNetscapeFuncs *host_functions);
-
-  // Initialize this PluginTest based on the arguments from NPP_New.
-  NPError New(uint16 mode,
-              int16 argc,
-              const char* argn[],
-              const char* argv[],
-              NPSavedData* saved) override;
-};
-
-}  // namespace NPAPIClient
-
-#endif  // CONTENT_TEST_PLUGIN_PLUGIN_PRIVATE_TEST_H_