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

BUILD.gn

 # Copyright 2014 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.
 
 import("//build_overrides/v8.gni")
 import("//testing/test.gni")
 import("pdfium.gni")
 
 config("pdfium_config") {
   cflags = []
@@ skipping 719 matching lines @@
     "core/src/fpdfapi/fpdf_parser/fpdf_parser_decode_unittest.cpp",
     "core/src/fpdfapi/fpdf_parser/fpdf_parser_parser_unittest.cpp",
     "core/src/fpdftext/fpdf_text_int_unittest.cpp",
     "core/src/fxcodec/codec/fx_codec_jpx_unittest.cpp",
     "core/src/fxcrt/fx_basic_bstring_unittest.cpp",
     "core/src/fxcrt/fx_basic_memmgr_unittest.cpp",
     "core/src/fxcrt/fx_basic_wstring_unittest.cpp",
     "core/src/fxcrt/fx_bidi_unittest.cpp",
     "core/src/fxcrt/fx_extension_unittest.cpp",
     "core/src/fxcrt/fx_system_unittest.cpp",
-    "third_party/base/nonstd_unique_ptr_unittest.cpp",
   ]
   deps = [
     "//testing/gtest",
     "//testing/gtest:gtest_main",
     ":pdfium",
     ":test_support",
   ]
   configs += [ ":pdfium_config" ]
 }
 
@@ skipping 35 matching lines @@
       "//v8:v8_libplatform",
     ]
     include_dirs += [
       "//v8",
       "//v8/include",
     ]
     configs += [ "//v8:external_startup_data" ]
   }
   configs += [ ":pdfium_config" ]
 }