Use incognito split for ChromeVox and TTS in Guest mode

chrome/browser/resources/chromeos/speech_synthesis/manifest.json

 {
+  // NOTE: Keep two json files in this directory in sync. The only difference
+  // should be incognito:split in Guest mode version.
   "name": "Chrome OS built-in text-to-speech extension",
   "version": "0.0.2",
   "description": "Text-to-speech (TTS) voice extension using Native Client technology.",
   "manifest_version": 2,
   "background": {
     "scripts": [
       "voice_data_hmm_de-DE.js",
       "voice_data_hmm_en-GB.js",
       "voice_data_hmm_en-US.js",
       "voice_data_hmm_es-ES.js",
@@ skipping 42 matching lines @@
       },
       {
         "voice_name": "Chrome OS Spanish",
         "lang": "es-ES",
         "gender": "female",
         "event_types": [ "start", "word", "end", "error" ]
       }
     ]
   }
 }