Add ChromeVox panel and implement caption display functionality.

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,
+    'is_chromeos%': 1,

[Peter Lundblad, 2015/11/06 15:00:58]

We already have a variable in gyp called 'chromeos', so it is a bit confusing to
add 'is_chromeos'. I think I understand why you do this, but it needs to be
clarified somehow. Perhaps a variable like chromevox_non_chromeos_build makes
more
sense.

[dmazzoni, 2015/11/06 21:01:01]

I ended up getting rid of the accessibilityFeatures permission because it turned
out to not reliably close ChromeVox. Apparently only one extension can have
"write" permission for a Chrome setting at a time.

Now clicking the 'close' button triggers the C++ code that hosts the panel to
close it, and that's reliable.

We'll have to figure out what to do for the webstore version. I could just hide
the close button.

   },
   '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=<(chromevox_extension_key)',
+        '--is_chromeos=<(is_chromeos)',
         '--is_chromevox_classic=<(is_chromevox_classic)',
         '--is_js_compressed=<(chromevox_compress_js)',
         '--set_version=<(version_full)',
         '--output_manifest=<(output_manifest_path)',
         '<(template_manifest_path)',
       ],
     },
   ],
 }