Add nonstd::unique_ptr as a workaround until std::unique_ptr is allowed.

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.
 
 {
   'targets': [
     {
       'target_name': 'bigint',
       'type': 'static_library',
       'sources': [
@@ skipping 48 matching lines @@
         'freetype/src/type1/type1.c',
         'freetype/src/cid/type1cid.c',
       ],
     },
     {
       'target_name': 'pdfium_base',
       'type': 'none',
       'sources': [
         'base/logging.h',
         'base/macros.h',
+        'base/nonstd_unique_ptr.h'
         'base/template_util.h',
         'base/numerics/safe_conversions.h',
         'base/numerics/safe_conversions_impl.h',
         'base/numerics/safe_math.h',
         'base/numerics/safe_math_impl.h',
       ],
     },
   ],
 }