Work around gyp nested merge problem in shim_headers.gypi.

build/shim_headers.gypi

 # Copyright (c) 2012 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.
 
 # This file is meant to be included into a target to handle shim headers
 # in a consistent manner. To use this the following variables need to be
 # defined:
 #   headers_root_path: string: path to directory containing headers
 #   header_filenames: list: list of header file names
 
 {
   'variables': {
     'shim_headers_path': '<(SHARED_INTERMEDIATE_DIR)/shim_headers/<(_target_name)/<(_toolset)',
     'shim_generator_additional_args%': [],
   },
   'include_dirs++': [
     '<(shim_headers_path)',
   ],
   'all_dependent_settings': {
     'include_dirs+++': [
       '<(shim_headers_path)',
     ],
+    'include_dirs++++': [
+      '<(shim_headers_path)',
+    ],
   },
   'actions': [
     {
       'variables': {
         'generator_path': '<(DEPTH)/tools/generate_shim_headers/generate_shim_headers.py',
         'generator_args': [
           '--headers-root', '<(headers_root_path)',
           '--output-directory', '<(shim_headers_path)',
           '<@(shim_generator_additional_args)',
           '<@(header_filenames)',
         ],
       },
       'action_name': 'generate_<(_target_name)_shim_headers',
       'inputs': [
         '<(generator_path)',
       ],
       'outputs': [
         '<!@pymod_do_main(generate_shim_headers <@(generator_args) --outputs)',
       ],
       'action': ['python',
                  '<(generator_path)',
                  '<@(generator_args)',
                  '--generate',
       ],
       'message': 'Generating <(_target_name) shim headers.',
     },
   ],
 }