WebUI: Enable ESLint rule for missing semicolons.

chrome/browser/resources/cleanup_tool/cleanup_browser_proxy.js

 // Copyright 2017 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.
 
 /**
  * @fileoverview Helper object and related behavior that encapsulate messaging
  * between JS and C++ for interacting with the Chrome Cleanup Tool.
  */
 
 /**
@@ skipping 56 matching lines @@
     },
     /** @override */
     startCleanup: function() {
       return cr.sendWithPromise('startCleanup');
     },
   };
 
   return {
     CleanupBrowserProxy: CleanupBrowserProxy,
     CleanupBrowserProxyImpl: CleanupBrowserProxyImpl,
-  }
+  };
 });