unbundle: provide shim headers for system ffmpeg

build/linux/unbundle/ffmpeg.gyp

 # Copyright 2013 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.
 
 {
   'targets': [
     {
       'target_name': 'ffmpeg',
       'type': 'none',
       'direct_dependent_settings': {
@@ skipping 23 matching lines @@
               '#include <libavcodec/avcodec.h>\n'
               'int test() { struct AVFrame frame;\n'
               'return av_frame_get_channels(&frame); }" '
               '--on-failure -DCHROMIUM_NO_AVFRAME_CHANNELS=1)',
         ],
         'defines': [
           '__STDC_CONSTANT_MACROS',
           'USE_SYSTEM_FFMPEG',
         ],
       },
+      'variables': {
+        'headers_root_path': '.',
+        'header_filenames': [
+          'libavcodec/avcodec.h',
+          'libavformat/avformat.h',
+          'libavutil/imgutils.h',
+        ],
+      },
+      'includes': [
+        '../../build/shim_headers.gypi',
+      ],
       'link_settings': {
         'ldflags': [
           '<!@(pkg-config --libs-only-L --libs-only-other libavcodec libavformat libavutil)',
         ],
         'libraries': [
           '<!@(pkg-config --libs-only-l libavcodec libavformat libavutil)',
         ],
       },
     },
   ],
 }