Check in pnglibconf.h so we don't need to generate it.

gyp/libpng.gyp

Index: gyp/libpng.gyp
diff --git a/gyp/libpng.gyp b/gyp/libpng.gyp
index 96120a8a618a9f79201c3ecdaab19eb1ffbdd65a..1ca6eef25343498577152b422f2c8ebf48c4c573 100644
--- a/gyp/libpng.gyp
+++ b/gyp/libpng.gyp
@@ -16,6 +16,8 @@
             'type': 'static_library',
             'include_dirs': [
               '../third_party/externals/libpng',
+              # Needed for generated pnglibconf.h
+              '../third_party/libpng',
             ],
             'dependencies': [
               'zlib.gyp:zlib',
@@ -26,6 +28,8 @@
             'direct_dependent_settings': {
               'include_dirs': [
                 '../third_party/externals/libpng',
+                # Needed for generated pnglibconf.h
+                '../third_party/libpng',
               ],
             },
             'cflags': [
@@ -42,22 +46,6 @@
                 ],
               }],
             ],
-            'actions': [
-              {
-                'action_name': 'generate_pngconf',
-                'variables' : {
-                  'prebuilt': '../third_party/externals/libpng/scripts/pnglibconf.h.prebuilt',
-                  'generated': '../third_party/externals/libpng/pnglibconf.h',
-                },
-                'inputs': [
-                  '<(prebuilt)',
-                ],
-                'outputs': [
-                  '<(generated)',
-                ],
-                'action': ['python', 'copy_file.py', '<(prebuilt)', '<(generated)'],
-              },
-            ],
             'sources': [
               '../third_party/externals/libpng/png.c',
               '../third_party/externals/libpng/pngerror.c',