Add SkDrawPosTextHCommand JSON, fix skiaserve build.

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',
-      ],
-    },
-  ],
-}