Add ChromeVox panel and implement caption display functionality.

chrome/browser/resources/chromeos/chromevox/chromevox_assets.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.
 
 {
   'variables': {
     'chromevox_assets_chromevox': [
       'chromevox/chromevox-128.png',
       'chromevox/chromevox-16.png',
       'chromevox/chromevox-19.png',
       'chromevox/chromevox-48.png',
+      'chromevox/close-19.png',

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

Perhaps create an images directory now that we're getting mroe of these
just to keep the top-level unpoluted.

[dmazzoni, 2015/11/06 21:01:00]

Done.

I realized the ChromeVox icons weren't in the manifest, so I remedied that. We
don't technically need them for the Chrome OS version, but we should really have
them in the web store version.

+      'chromevox/close-hover-19.png',
+      'chromevox/options-19.png',
+      'chromevox/options-hover-19.png',
+      'chromevox/triangle-6.png',
     ],
     'chromevox_assets_chromevox_background_earcons': [
       'chromevox/background/earcons/alert_modal.ogg',
       'chromevox/background/earcons/alert_nonmodal.ogg',
       'chromevox/background/earcons/button.ogg',
       'chromevox/background/earcons/check_off.ogg',
       'chromevox/background/earcons/check_on.ogg',
       'chromevox/background/earcons/editable_text.ogg',
       'chromevox/background/earcons/invalid_keypress.ogg',
       'chromevox/background/earcons/link.ogg',
@@ skipping 102 matching lines @@
         {
           'destination': '<(chromevox_dest_dir)/cvox2/background/earcons',
           'files': [
             '<@(chromevox_assets_cvox2_background_earcons)',
           ],
         },
       ],
     },
   ],
 }