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

gyp/bench.gypi

 # Copyright 2015 Google Inc.
 #
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 {
   'include_dirs': [
     '../bench/subset',
     '../bench',
+    '../include/private',
     '../src/core',
     '../src/effects',
     '../src/gpu',
     '../src/utils',
     '../tools',
   ],
   'sources': [ '<!@(python find.py ../bench "*.cpp")' ],
 
   'dependencies': [
     'etc1.gyp:libetc1',
     'skia_lib.gyp:skia_lib',
     'tools.gyp:resources',
     'tools.gyp:sk_tool_utils',
   ],
   'conditions': [
     ['skia_gpu == 1', {
       'include_dirs': [ '../src/gpu' ],
       'dependencies': [ 'gputest.gyp:skgputest' ],
     }],
     ['not skia_android_framework', {
         'sources!': [ '../bench/nanobenchAndroid.cpp' ],
     }],
   ],
 }