(WIP) Use generator to generate externs for chrome.fileManagerPrivate API.

ui/file_manager/image_loader/compiled_resources.gyp

 # Copyright 2014 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': 'background',
       'variables': {
         'depends': [
           '../../webui/resources/js/assert.js',
           '../file_manager/common/js/file_type.js',
           '../file_manager/common/js/metrics_base.js',
           '../file_manager/common/js/metrics.js',
           '../file_manager/common/js/metrics_events.js',
           '../file_manager/foreground/js/metadata/image_orientation.js',
           'cache.js',
           'image_loader.js',
           'piex_loader.js',
           'request.js',
           'scheduler.js',
         ],
         'externs': [
           '<(EXTERNS_DIR)/chrome_extensions.js',
           '<(EXTERNS_DIR)/file_manager_private.js',
+          '<(EXTERNS_DIR)/manifest_types.js',
           '<(EXTERNS_DIR)/metrics_private.js',
           '../../../third_party/analytics/externs.js',
         ],
       },
       'includes': [
         '../compile_js.gypi',
       ],
     }
   ],
 }