Added checkbox in MetaMask doesn't appear

I modified MetaMask, commit hash e8232aa714df59726b2e476c2d9e80bae6827f32 adding a new checkbox. But the checkbox does not appear when I install the extension from a folder into a browser. What did I do wrong?

$ git diff
diff --git a/app/_locales/en/messages.json b/app/_locales/en/messages.json
index 94c9e49f3..ba1405945 100644
--- a/app/_locales/en/messages.json
+++ b/app/_locales/en/messages.json
@@ -1502,6 +1502,9 @@
   "gasUsed": {
     "message": "Gas used"
   },
+  "gasless": {
+    "message": "Gasless token"
+  },
   "gdprMessage": {
     "message": "This data is aggregated and is therefore anonymous for the purposes of General Data Protection Regulation (EU) 2016/679. For more information in relation to our privacy practices, please see our $1.",
     "description": "$1 refers to the gdprMessagePrivacyPolicy message, the translation of which is meant to be used exclusively in the context of gdprMessage"
diff --git a/ui/pages/import-token/import-token.component.js b/ui/pages/import-token/import-token.component.js
index 5c4a43c04..093801fe1 100644
--- a/ui/pages/import-token/import-token.component.js
+++ b/ui/pages/import-token/import-token.component.js
@@ -25,6 +25,7 @@ import { TOKEN_STANDARDS } from '../../../shared/constants/transaction';
 import { STATIC_MAINNET_TOKEN_LIST } from '../../../shared/constants/tokens';
 import TokenSearch from './token-search';
 import TokenList from './token-list';
+import CheckBox from '../../components/ui/check-box';
 
 const emptyAddr = '0x0000000000000000000000000000000000000000';
 
@@ -569,6 +570,11 @@ class ImportToken extends Component {
             className="import-token__decimal-warning"
           />
         )}
+        <CheckBox
+          id="custom-gasless"
+          label={t('gasless')}
+          margin="normal"
+        />
       </div>
     );
   }