Make select-to-speak work with Google Docs.

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

 {
 {%if key is defined %}
   "key": "{{key}}",
 {% endif %}
   "manifest_version": 2,
   "name": "__MSG_SELECT_TO_SPEAK_NAME__",
   "version": "{{set_version}}",
   "description": "__MSG_SELECT_TO_SPEAK_DESCRIPTION__",
 {% if is_guest_manifest == '1' %}
   "incognito": "split",
 {% endif %}
   "background": {
     "scripts": [
       "select_to_speak.js",
       "select_to_speak_main.js"
     ]
   },
   "permissions": [
     "accessibilityPrivate",
     "storage",
     "tts"
   ],
   "automation": {
     "desktop": true
   },
   "default_locale": "en",
-  "options_page": "options.html"
+  "options_page": "options.html",
+  "content_scripts": [
+    {
+      "matches": [ "https://docs.google.com/document*" ],
+      "js": [
+        "select_to_speak_gdocs_script.js"
+      ]
+    }
+  ]
 }