add -Iinclude/private anywhere we have -Isrc/core

gyp/ports.gyp

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 # Port-specific Skia library code.
 {
   'targets': [
     {
       'target_name': 'ports',
       'product_name': 'skia_ports',
       'type': 'static_library',
       'standalone_static_library': 1,
       'dependencies': [
         'core.gyp:*',
       ],
       'include_dirs': [
         '../include/effects',
         '../include/images',
         '../include/ports',
+        '../include/private',
         '../include/utils',
         '../include/utils/win',
         '../src/core',
         '../src/lazy',
         '../src/ports',
         '../src/sfnt',
         '../src/utils',
       ],
       'sources': [
         '../src/ports/SkDebug_stdio.cpp',
@@ skipping 178 matching lines @@
         }],
       ],
       'direct_dependent_settings': {
         'include_dirs': [
           '../include/ports',
         ],
       },
     },
   ],
 }