JSON schema compiler can't handle strings as types

chrome/common/extensions/api/api.gyp

 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 {
   'targets': [
     {
       'target_name': 'api',
       'type': 'static_library',
       'sources': [
         '<@(idl_schema_files)',
         '<@(json_schema_files)',
       ],
       'includes': [
         '../../../../build/json_schema_bundle_compile.gypi',
         '../../../../build/json_schema_compile.gypi',
       ],
       'variables': {
         'chromium_code': 1,
         'json_schema_files': [
           'browserAction.json',
           'experimental.declarative.json',
+          'experimental.fontSettings.json',
           'permissions.json',
           'storage.json',
           'tabs.json',
           'windows.json',
         ],
         'idl_schema_files': [
           'experimental.alarms.idl',
           'experimental.bluetooth.idl',
           'experimental.dns.idl',
           'experimental.serial.idl',
           'experimental.socket.idl',
         ],
         'cc_dir': 'chrome/common/extensions/api',
         'root_namespace': 'extensions::api',
       },
     },
   ],
 }