Switch from nonstd::unique_ptr to std::unique_ptr.

third_party/third_party.gyp

 # Copyright 2014 PDFium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'target_defaults': {
     'defines': [
       'OPJ_STATIC',
       '_CRT_SECURE_NO_WARNINGS',
     ],
@@ skipping 268 matching lines @@
         'zlib_v128/uncompr.c',
         'zlib_v128/zutil.c',
       ],
     },
     {
       'target_name': 'pdfium_base',
       'type': 'none',
       'sources': [
         'base/logging.h',
         'base/macros.h',
-        'base/nonstd_unique_ptr.h',
         'base/numerics/safe_conversions.h',
         'base/numerics/safe_conversions_impl.h',
         'base/numerics/safe_math.h',
         'base/numerics/safe_math_impl.h',
         'base/stl_util.h',
         'base/template_util.h',
       ],
     },
   ],
 }