support for more features when rendering to/from JSON

gyp/json.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.
 {
   'targets': [
     {
       'target_name': 'json',
       'product_name': 'skia_json',
       'type': 'static_library',
       'standalone_static_library': 1,
       'dependencies': [
         'core.gyp:core',
         'jsoncpp.gyp:jsoncpp',
       ],
       'include_dirs': [
         '../include/core',
         '../include/effects',
+        '../include/private',
         '../include/utils',
         '../src/core',
       ],
       'sources': [
         '../tools/json/SkJSONCanvas.cpp',
         '../tools/json/SkJSONRenderer.cpp',
       ],
     },
   ],
 }