Only inject ChromeVox classic when necessary.

chrome/browser/resources/chromeos/chromevox/manifest.json.jinja2

 {
 {%if key is defined %}
   "key": "{{key}}",
 {% endif %}
   "manifest_version": 2,
   "name": "ChromeVox",
   "version": "{{set_version}}",
   "description": "ChromeVox - Giving Voice to Chrome.",
 {% if is_guest_manifest == '1' %}
   "incognito": "split",
@@ skipping 15 matching lines @@
     "commandLinePrivate",
     "experimental",
     "history",
     "storage",
     "systemPrivate",
     "tabs",
     "tts",
     "virtualKeyboardPrivate",
     "<all_urls>"
   ],
+{% if use_chromevox_next == '0' %}
   "content_scripts": [
     {
       "matches": [ "<all_urls>" ],
       "exclude_globs": [ "chrome-extension://mndnfokpggljbaajbnioimlmbfngpief/chromevox/background/background.html" ],
       "all_frames": true,
       "js": [
         "chromeVoxChromePageScript.js"
       ]
     }
   ],
-  "web_accessible_resources": [
+{% endif %}
+"web_accessible_resources": [
     "chromevox/injected/api.js",
     "chromevox/injected/api_util.js",
     "chromevox/injected/mathjax.js",
     "chromevox/injected/mathjax_external_util.js"
   ],
 {% if use_chromevox_next == '1' %}
   "automation": {
     "desktop": true
   },
   "commands": {
@@ skipping 43 matching lines @@
       "description": "Moves to the previous heading",
       "suggested_key": {
         "chromeos": "Search+Shift+H"
       }
     }
   },
 {% endif %}
   "options_page": "chromevox/background/options.html",
   "default_locale": "en"
 }