Move headers used by headers in include/ to include/private.

gyp/example.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.
 # GYP file to build hello world example.
 {
   'includes': [
     'apptype_console.gypi',
   ],
   'targets': [
     {
       'target_name': 'HelloWorld',
       'type': 'executable',
       'include_dirs' : [
+        '../include/private',
         '../include/gpu',
       ],
       'sources': [
         '../example/HelloWorld.h',
         '../example/HelloWorld.cpp',
       ],
       'dependencies': [
         'skia_lib.gyp:skia_lib',
         'views.gyp:views',
       ],
     },
   ],
 }