Port chromevox build to GN.

chrome/browser/resources/chromeos/chromevox/generate_manifest.gypi

 # 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.
 
 # Generates an output manifest based on a Jinja2 templated manifest.
 # Include this file inside of your target to generate a manifest.
 # The following variables must be set before including this file:
 #
 # template_manifest_path: a valid Jinja2 file path.
 # output_manifest_path: file path for the resulting manifest.
+# chromevox_extension_key: The extension key to include in the manifest.
 #
 # The following variables are optional:
 #
 # is_guest_manifest: 1 or 0; generates a manifest usable while in guest
 # mode.
 # is_chromevox_classic: 1 or 0; generates a manifest for ChromeVox Classic.
 # chromevox_compress_js: 1 or 0; whether the javascript is compressed.
 
 {
   'variables': {
     'generate_manifest_script_path': 'tools/generate_manifest.py',
     'is_guest_manifest%': 0,
     'is_chromevox_classic%': 0,
-    'key': 'MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDltVl1k15pjRzuZfMc3B69inxwm2bZeZ2O8/zFO+NluHnBm3GJ3fzdOoFGJd+M16I8p7zxxQyHeDMfWYASyCeB8XnUEDKjqNLQfCnncsANzHsYoEbYj2nEUML2P13b9q+AAvpCBpAJ4cZp81e9n1y/vbSXHE4385cgkKueItzikQIDAQAB',
   },
   'includes': [
     '../../../../../build/util/version.gypi',
   ],
   'actions': [
     {
       'action_name': 'generate_manifest',
       'message': 'Generate manifest for <(_target_name)',
       'inputs': [
         '<(generate_manifest_script_path)',
         '<(template_manifest_path)',
       ],
       'outputs': [
         '<(output_manifest_path)'
       ],
       'action': [
         'python',
         '<(generate_manifest_script_path)',
         '--is_guest_manifest=<(is_guest_manifest)',
-        '--key=<(key)',
+        '--key=<(chromevox_extension_key)',
         '--is_chromevox_classic=<(is_chromevox_classic)',
         '--is_js_compressed=<(chromevox_compress_js)',
         '--set_version=<(version_full)',
         '--output_manifest=<(output_manifest_path)',
         '<(template_manifest_path)',
       ],
     },
   ],
 }